Chemical bonding method non-woven fabric preparation method for enhancing strength by using chitosan and non-woven fabric prepared by method

Abstract

The invention belongs to the technical field of non-woven fabrics, and discloses a chemical bonding method non-woven fabric preparation method using chitosan to enhance strength, and the method comprises the following steps: preparing a fiber raw material composed of main body fibers and chitosan fibers, respectively opening the main body fibers and the chitosan fibers, uniformly mixing, and carding to form a uniform fiber web; applying an anionic acrylic latex to the web; performing drying and hot rolling treatment on the fiber net, so that the latex is self-crosslinked, and anionic groups of the latex and cationic active groups of the chitosan fibers form an ionic bonding and chemical crosslinking dual-crosslinking structure; and cooling, trimming and winding to obtain the non-woven fabric. According to the invention, a latex self-crosslinking and ionic bonding / chemical crosslinking dual-crosslinking structure is adopted, and the anionic acrylic latex and the chitosan fibers are pertinently matched, so that the latex can be self-crosslinked to form a network and form stable ionic bonding and / or chemical crosslinking with the cationic fibers, and the binding force between the fibers is greatly enhanced; the problem that traditional non-woven fabric is insufficient in strength is solved.

Description

Technical Field

[0001] This application relates to the field of nonwoven fabric technology, and more specifically, to a method for preparing nonwoven fabric using a chemical bonding method that utilizes chitosan to enhance strength. Background Technology

[0002] In the field of nonwoven fabric manufacturing, chemical bonding methods are widely used due to their unique properties and diverse applications, especially in medical and health, industrial filtration, civil engineering, agriculture, and home furnishing. Currently, chemical bonding methods for nonwoven fabrics typically involve applying adhesives to the fiber web through impregnation, spraying, or foam coating. The adhesive is then cured through drying and baking processes, thus achieving bonding between the fibers. Commonly used adhesives are primarily acrylate-based, which mainly form a polymer film through their own cross-linking reaction, thereby bonding the fibers together.

[0003] However, traditional chemical bonding methods for preparing nonwoven fabrics have limitations in terms of strength, bonding firmness, environmental friendliness, and production efficiency. Firstly, the interaction between existing adhesives and fibers is mostly physical entanglement or hydrogen bonding, which can limit bonding strength and lead to performance degradation under specific operating conditions (such as humid and hot conditions). This results in nonwoven fabrics with insufficient bonding strength and durability to meet the demands of high-strength applications. Secondly, in traditional chemical bonding processes, the affinity between the adhesive and fibers is poor, leading to uneven bonding. The fibers used in traditional chemical bonding processes are mostly hydrophilic materials such as viscose fibers. When these fibers encounter moisture in the acrylic emulsion during sizing, they absorb water and swell; during drying, they dehydrate and shrink. This physical expansion and contraction firstly prevents uniform coverage during the initial sizing process, and later, during dehydration and drying, the shrinkage due to water loss causes significant relative displacement between fibers, disrupting the adhesion points and affecting the overall consistency of the nonwoven fabric's performance. Finally, because the carding method of chemically bonded nonwoven fabrics results in fibers being mostly arranged radially, the transverse tensile strength mainly relies on the properties of the adhesive. This leads to a significant difference between the radial and transverse tensile strength of the finished product, and insufficient transverse tensile strength causing damage to the nonwoven fabric has become a pain point in the industry. These technical problems and gaps limit the application of chemically bonded nonwoven fabrics in broader and more demanding fields.

[0004] Cationic fibers have a history of application in various nonwoven fabric manufacturing processes, mainly in two aspects: 1. As a functional component, primarily used for dyeing and appearance. Due to their different affinities for dyes, they can exhibit drastically different colors in the same dyeing process. This is the most direct and primary use of cationic fibers. 2. As an identification fiber. Under specific online monitoring systems (such as cameras and sensors), normal products mixed with cationic fibers will present a background signal, while defects composed purely of the base material (such as unevenly mixed clumps) will be easily identified and automatically rejected by the system due to the lack of this signal. This greatly improves production quality and efficiency.

[0005] However, the applications of cationic fibers mentioned above are limited to manufacturing processes such as spunlace, needle punching, and spunbonding, rather than chemically bonded nonwoven fabric production. In traditional chemical bonding, cationic fibers (such as ordinary cationic dyeable polyester) cannot function because the cationic groups are shielded by the anionic environment of the latex. Therefore, there is no precedent for using cationic fibers in chemically bonded nonwoven fabric products.

[0006] In view of this, we propose a chemical bonding method for preparing nonwoven fabrics that utilizes chitosan to enhance strength. Summary of the Invention

[0007] 1. The technical problems to be solved.

[0008] The purpose of this application is to provide a method for preparing nonwoven fabrics using a chemical bonding method that enhances strength with chitosan. This method solves the technical problems mentioned in the background art and achieves a dual cross-linking structure through latex self-crosslinking + ionic bonding / chemical crosslinking. By specifically combining anionic acrylic latex with chitosan fibers, the latex can not only crosslink itself to form a network, but also form stable ionic bonding and / or chemical crosslinking with cationic fibers, which greatly enhances the bonding force between fibers and solves the problem of insufficient strength in traditional nonwoven fabrics.

[0009] 2. Technical solution.

[0010] This application provides a method for preparing nonwoven fabric using a chemical bonding method that enhances strength with chitosan, including the following steps.

[0011] Step 1, Raw material preparation and pretreatment: Screen the main fiber and chitosan-based cationic reinforcing fiber, and control parameters such as degree of deacetylation, mixing ratio, and fiber specifications; perform pre-opening, modification, and antistatic treatment on the fiber to ensure fiber dispersibility and activity.

[0012] In one possible implementation, the cationic fiber is incorporated in an amount of 0.5-20% of the total weight of the fiber raw material; the chitosan fiber is a fiber material containing chitosan-like materials with a specific degree of deacetylation on its surface or inside, and as the core type of cationic reinforced fiber, its incorporation ratio also conforms to the above range.

[0013] Step 2, Opening and Uniform Mixing: The pretreated main fibers and chitosan-based cationic reinforcing fibers are fully opened separately and then mixed in proportion; corresponding mixing methods are used for different addition amounts to ensure that the cationic reinforcing fibers are uniformly dispersed in the main fibers.

[0014] Step 3, Combing into a Web: The uniformly mixed composite fibers are combed and laid into a fiber web with uniform thickness and density. The basis weight and web laying method are controlled to provide a stable base for subsequent latex bonding.

[0015] Step 4, Latex Application: Select anionic acrylic latex and apply it evenly to the fiber mesh through methods such as impregnation, spraying, foam impregnation, and scraping, so that the latex and chitosan-reinforcing fibers can be in full contact, preparing for the cross-linking reaction.

[0016] In one possible embodiment, the anionic acrylic latex is an acrylate copolymer emulsion with self-crosslinking function; its molecular chain contains one or more anionic groups, such as carboxyl groups (-COOH) and sulfonic acid groups (-SO3H).

[0017] In one possible implementation, when anionic acrylic latex is applied to the fiber web, ultrasonic-assisted polymerization technology can be used to promote uniform dispersion and reaction of monomers, thereby improving polymerization efficiency.

[0018] Step 5, Drying and Baking: Temperature-controlled drying and baking achieves self-crosslinking of latex and ionic / chemical crosslinking between latex and chitosan fibers, forming a high-strength adhesive network.

[0019] In one possible implementation, the drying and baking treatment is carried out at a temperature of 120°C-180°C for 3-20 minutes. Under these conditions, while the anionic acrylic latex completes its own cross-linking, the anionic groups on its molecular chain undergo ionic bonding and / or chemical cross-linking reactions with the cationic active groups on the chitosan fibers, further enhancing the strength of the nonwoven fabric.

[0020] Step 6, Post-processing: After cooling and shaping, trimming and winding, inspection and packaging, the finished product is obtained.

[0021] 3. Beneficial effects.

[0022] One or more technical solutions provided in this application have at least the following technical effects or advantages.

[0023] (1) This invention breaks the conventional understanding in the field that cationic fibers fail in chemical bonding processes. For the first time, chitosan fibers with a specific degree of deacetylation (40%-95%) are selected as reinforcing fibers. The degree of deacetylation and the mixing ratio are precisely controlled to ensure that the cationic active groups can effectively participate in the reaction and avoid agglomeration.

[0024] (2) Dual cross-linking mechanism: The latex self-cross-linking + ionic bonding / chemical cross-linking dual cross-linking structure is designed. Through the targeted combination of anionic acrylic latex and chitosan fibers, the latex can not only cross-link itself to form a network, but also form stable ionic bonding and / or chemical cross-linking with cationic fibers, which greatly strengthens the bonding force between fibers and solves the problem of insufficient strength of traditional non-woven fabrics.

[0025] (3) Synergistic optimization of performance and practicality: While improving strength, the defects of increasing the amount of adhesive or adding inorganic fillers are avoided. The prepared non-woven fabric has the advantages of high strength, soft hand feel, uniform bonding, good air permeability, environmental protection and biodegradability (chitosan fiber is biodegradable), and the production cost is controllable. The raw materials and parameters can be adjusted according to different needs to adapt to a variety of application scenarios. Attached Figure Description

[0026] Figure 1 Example diagram of the structure of the cross-linked product of acrylic acid chitosan generated by the reaction of acrylic latex and chitosan.

[0027] Figure 2 The chart shows different weights of the fiber web formed by the precision carding machine in Example 8.

[0028] Figure 3 The graph shows the average breaking strength of the fiber web in the length and width directions in Example 8.

[0029] Figure 4 The chart shows the data of viscose fiber and chitosan fiber in different experimental groups in Example 9.

[0030] Figure 5 This is a chart of lateral tensile force test data from Example 9.

[0031] Figure 6 The chart shows the data of lyocell fiber and chitosan fiber in different experimental groups in Example 10.

[0032] Figure 7 This is a chart showing the results of the lateral tensile force test in Example 10.

[0033] Figure 8 Images shown are from a tensile test.

[0034] Figure 9 The chart shows the experimental results of Group A in Example 10.

[0035] Figure 10 The chart shows the experimental results of Group B in Example 10.

[0036] Figure 11 This is an electron microscope image of a nonwoven fabric sample containing 5% chitosan fiber. Detailed Implementation

[0037] The present application will be further described in detail below with reference to the accompanying drawings.

[0038] An unexpected discovery revealed that fibers prepared from chitosan and its derivatives with specific degrees of deacetylation can effectively improve the mechanical strength of chemically bonded nonwoven fabrics, especially the wet strength and transverse strength of the nonwoven fabrics.

[0039] Reference Figure 1 This application provides a method for preparing nonwoven fabric using a chemical bonding method that enhances strength with chitosan, comprising the following steps.

[0040] Step 1: Raw material preparation and pretreatment: Select suitable fiber raw materials, accurately control raw material parameters, and ensure fiber dispersibility and activity through pretreatment to lay the foundation for subsequent mixing, bonding and strength improvement, and avoid strength shortcomings caused by poor raw material compatibility and uneven dispersion.

[0041] 1.1 Fiber Raw Material Preparation: The composite fiber raw material is prepared by blending the main fiber and cationic reinforcing fiber in a predetermined ratio. The main fiber serves as the structural skeleton of the nonwoven fabric, providing basic forming properties; the cationic reinforcing fiber acts as the strength-enhancing core, containing chitosan-like materials with a specific degree of deacetylation on its surface or inside. This allows for a specific reaction with the subsequent anionic latex, strengthening the adhesion between fibers. For hydrophobic main fibers such as polyester, plasma modification treatment is required beforehand to improve their surface hydrophilicity, ensuring compatibility with the latex and cationic reinforcing fiber, and avoiding insufficient adhesion due to hydrophobicity.

[0042] Specifically, the cationic reinforcing fibers are selected from chitosan fibers or their derivatives, preferably those possessing both cationic activity and fiber flexibility, including but not limited to: carboxymethyl chitosan fibers, hydroxybutyl chitosan fibers, hydroxypropyl chitosan fibers, and quaternary ammonium salt chitosan fibers. The selection can be flexible based on the application scenario of the nonwoven fabric; for example, hydroxybutyl chitosan fibers are preferred for humid environments, while carboxymethyl chitosan fibers are preferred for hygiene products. Chitosan fibers must be stored in a sealed environment at 20℃±5℃ and 50%±5% humidity to prevent moisture absorption and degradation; the degree of deacetylation between different batches of chitosan fibers must be ≤±3% to ensure batch consistency.

[0043] 1.2 Raw material parameter control: To ensure a balance between reinforcement effect, molding performance and production cost, the following three core parameters are strictly controlled, and each parameter works together.

[0044] (1) Deacetylation requirements: The deacetylation degree of chitosan fibers is strictly controlled between 40% and 95% to ensure that the number of cationic active groups (-NH3+, quaternary ammonium salt groups, etc.) on the fiber surface is appropriate and can form stable ionic bonds with the anionic groups in the anionic latex. When the deacetylation is too low (<40%), the acetyl content on the surface of chitosan fibers is too high, the cationic active groups are not exposed enough, the reactivity with the anionic latex is low, and effective cross-linking adhesion cannot be formed, resulting in no significant strength enhancement effect; when the deacetylation is too high (>95%), the intermolecular hydrogen bonding of chitosan fibers is enhanced, the fiber solubility is poor and the flexibility is reduced, which not only makes it difficult to mix evenly with the main fiber, but also causes the fiber itself to break, which in turn affects the overall strength and hand feel of the nonwoven fabric. Therefore, chitosan fibers with a deacetylation degree of 50%-80% are preferred to balance activity and flexibility.

[0045] (2) Mixing ratio: The mixing ratio of cationic reinforced fiber is 0.5%-20% of the total weight of fiber raw materials, preferably 2.5%-8%. This ratio range is derived by taking into account the strength improvement effect, fiber dispersibility, product feel and production cost. The specific adaptation logic is as follows.

[0046] When the blending ratio is below 0.5%, the number of cationic reinforcing fibers is too small, resulting in insufficient total cationic active groups on their surface and limited reaction sites with anionic latex. This prevents the formation of a comprehensive cross-linking adhesive network, leading to a strength increase of less than 10% in the nonwoven fabric and failing to achieve the expected reinforcement effect. When the blending ratio is above 20%, the cationic reinforcing fibers are prone to agglomeration, especially since chitosan fibers themselves have a certain degree of viscosity and are difficult to disperse evenly in the main fibers. At the same time, a large number of cationic groups will preferentially combine with the anionic latex, resulting in a decrease in the self-crosslinking ratio of the latex itself. This leads to a decrease in the flexibility and breathability of the nonwoven fabric, a stiff feel, and a significant increase in raw material costs. However, within the preferred range of 2.5%-8%, the cationic reinforcing fibers can be evenly dispersed in the main fibers, forming sufficient reaction sites with the anionic latex. This not only increases the strength of the nonwoven fabric by more than 30% but also ensures a soft feel and good breathability while controlling raw material costs within a reasonable range.

[0047] (3) Fiber specifications: The specifications of the main fiber and the cationic reinforcing fiber must be matched to ensure uniform mixing and molding stability. The specific specifications are as follows.

[0048] The main fibers are selected from one or more of the following: polyester staple fiber, cotton fiber, polypropylene fiber, ES fiber, viscose fiber, aramid 1414 chopped fiber, lyocell fiber, etc. The specifications are uniformly controlled at 1.2D-3.0D (fineness) and 38mm-51mm in length. The main fibers in this specification range have moderate bulkiness and good spinnability, and can quickly form a uniform fiber web.

[0049] The cationic reinforcing fiber is controlled to have a size of 1.2D-2.0D and a length of 38mm-55mm. Its fineness is slightly lower than or equal to that of the main fiber, and its length is basically the same as that of the main fiber. The core purpose is to avoid stratification and uneven dispersion during mixing due to excessive size differences, and to ensure that an appropriate amount of cationic reinforcing fiber is distributed around each main fiber, so as to provide a guarantee for subsequent full bonding. For example, when the main fiber is selected as 1.5D×38mm polyester staple fiber, the cationic reinforcing fiber is preferably 1.2D×38mm chitosan fiber, which has the best matching degree.

[0050] 1.3 Raw material pretreatment: The main fiber and cationic reinforcing fiber are subjected to targeted pre-opening treatment to remove impurities and clumps from the fiber, so that the fiber is in a loose and dispersed state, while protecting the cationic activity of the cationic reinforcing fiber. The specific operation is as follows.

[0051] For the main fibers, conventional pre-opening equipment such as pre-opening machines and carding machines are used for processing. The opening force is moderate to remove dust, neps, impurities, etc. from the fibers, ensuring that the fibers are dissociated into loose single fibers or small fiber bundles, avoiding clumping that affects subsequent mixing and carding. If the main fibers are hydrophobic fibers such as polyester, plasma modification is required after pre-opening for 3-5 minutes to improve surface hydrophilicity.

[0052] For chitosan-derived fibers, such as hydroxypropyl chitosan fibers and carboxymethyl chitosan fibers, due to their poor flexibility, brittleness, and susceptibility to mechanical damage to surface-active groups, a gentle opening method should be adopted, reducing the opening force and speed. A small amount of antistatic agent, such as a nonionic surfactant, can be added to the opening equipment to prevent fiber agglomeration caused by static electricity generated by friction, while also preventing fiber damage that leads to a decrease in cationic activity. Specifically, polyethylene glycol-type nonionic surfactants are selected, with an addition amount of 0.1%-0.3% of the total fiber weight. For example, when gently opening hydroxypropyl chitosan fibers, adding 0.2% polyethylene glycol-type antistatic agent can effectively prevent static agglomeration. This antistatic agent needs to undergo compatibility testing with anionic latex in advance to ensure that it does not affect the self-crosslinking properties of the latex, and the residual amount of antistatic agent in the product must be ≤0.05%, meeting the safety standards for medical and hygiene products.

[0053] The pretreated fibers need to be placed in a constant temperature and humidity environment (25℃±5℃, 60%±10% humidity) for 2-4 hours to eliminate internal stress and ensure uniformity in subsequent opening and mixing. After standing, the fibers need to be inspected a second time to confirm that there is no agglomeration or clumping. If slight agglomeration is present, it needs to be slightly broken up before proceeding to the next step.

[0054] Step 2: Opening and mixing: Fully open and mix the two types of pretreated fibers to ensure that the cationic reinforcing fibers are evenly dispersed in the main fibers, forming a uniform composite fiber system and avoiding problems such as insufficient local reinforcement and local agglomeration and stiffness.

[0055] 2.1 Opening treatment: The pretreated main fiber and cationic reinforcing fiber are fully opened by an opening machine. The opening equipment is a high-yield opening machine or a carding needle opening machine. The opening parameters are adjusted according to the fiber type to ensure that the fibers are fully dissociated and formed into a single fiber state. The specific parameters are controlled as follows.

[0056] The opening speed should be controlled at 800-1200 r / min, and the opening time should be 5-15 min. For the main fibers, a higher speed and shorter time, such as 5-10 min, can be used to ensure sufficient opening without damaging the fibers. For cationic reinforced fibers, especially chitosan-derived fibers, a lower speed and longer time, such as 10-15 min, should be used to avoid fiber breakage while ensuring sufficient opening. A lower speed, such as 800-1000 r / min, is recommended. Specific adaptation standards: Quaternary ammonium salt chitosan fibers (40%-50% deacetylation), speed 900-1000 r / min, time 10-12 min; Chitosan fibers (80%-95% deacetylation), speed 800-900 r / min, time 12-15 min.

[0057] During the opening process, the fiber status needs to be observed in real time to ensure that there are no obvious clumps or unopened fiber bundles, and that the single fiber dissociation rate reaches more than 95%. If clumps are found, the machine needs to be stopped for cleaning and the opening process needs to be repeated to avoid affecting the subsequent mixing effect.

[0058] 2.2 Uniform Mixing: The opened main fibers and cationic reinforcing fibers are put into the cotton blending equipment according to the preset mixing ratio for uniform mixing. The cotton blending equipment can be flexibly selected according to the production scale and mixing accuracy, including but not limited to: cotton blending box, multi-compartment cotton blending machine, weighing automatic cotton blending system, etc. The specific mixing parameters are as follows.

[0059] The mixing time is 10-25 minutes, and the mixing speed is 300-500 r / min. The mixing time and speed should be matched. For example, when the mixing speed is 300 r / min, the mixing time should be controlled at 20-25 minutes; when the mixing speed is 500 r / min, the mixing time should be controlled at 10-15 minutes to ensure uniform mixing while avoiding damage to the fibers due to over-mixing.

[0060] For scenarios with a low proportion of cationic reinforcing fibers (≤2%), due to their small quantity and tendency to agglomerate, conventional mixing methods are insufficient to achieve uniform dispersion. Therefore, a special method of multiple-layer mixing and layered application is employed. Specifically, the main fiber is divided into 3-5 layers. A predetermined proportion of cationic reinforcing fibers is evenly spread on the surface of each layer. Then, each layer is fed into a mixing device, undergoing multiple layers of mixing and application. The amount of fibers applied each time is controlled at 30%-50% of the device's rated capacity. This ensures that the cationic reinforcing fibers are evenly dispersed in each layer of the main fiber, avoiding localized agglomeration or areas lacking reinforcing fibers, thus laying the foundation for uniform strength improvement. If the proportion of cationic reinforcing fibers exceeds 15%, it needs to be pre-mixed with a small amount of main fiber before mixing to form a masterbatch, which is then mixed with the remaining main fiber to reduce agglomeration.

[0061] After mixing, samples are taken to test the mixing uniformity. A random sampling method is used, taking 3-5 samples, each weighing 5g, and testing the actual proportion of cationic reinforcing fibers in each sample. If the proportion deviation is ≤±0.2%, it is considered to be mixed uniformly and can proceed to the next step; if the deviation is too large, the mixing process needs to be repeated.

[0062] Step 3: Combing into a web: Combing the uniformly mixed composite fibers into a fiber web with a uniform structure, consistent thickness, no holes, and no clumps, so that the fibers are arranged in the same direction or cross-arranged, to ensure that the subsequent latex is applied evenly and that the fibers are fully bonded together, thereby ensuring the uniform strength of the nonwoven fabric.

[0063] 3.1 Carding process: The uniformly mixed composite fiber raw material is fed into a carding machine. The carding machine is selected according to the performance requirements of the nonwoven fabric, including: high-speed carding machine, double doffer carding machine, heavy-duty carding machine, precision carding machine, etc.

[0064] During the carding process, the carding parameters are adjusted according to the basis weight of the target nonwoven fabric. The core parameters are controlled as follows: carding speed is 1500-2500 r / min, and carding spacing is 0.1-0.3 mm; for thin nonwoven fabrics (basis weight 25-40 g / m²), the carding parameters are adjusted accordingly. 2 Use a higher carding speed (2000-2500 r / min) and a smaller carding gap (0.1-0.2 mm) to ensure fine carding and uniform fiber arrangement; thick nonwoven fabric (60-100 g / m²) 2Choose a lower carding speed (1500-2000 r / min) and a larger carding spacing, such as 0.2-0.3 mm, to avoid damage caused by excessive carding of fibers, while ensuring uniform fiber web thickness.

[0065] The purpose of carding is to remove short fibers (<10mm in length) and residual impurities from the fibers, so that the composite fibers are evenly arranged in the same direction to form a dense fiber layer. During the carding process, the cotton knots and short fibers on the carding machine needle cloth need to be cleaned in real time to avoid clogging of the needle cloth and affecting the carding effect. The carded fiber layer should be fluffy and uniform, without obvious fiber bundles and impurities.

[0066] 3.2 Web Forming: The carded fiber layer is laid into a uniform fiber web using the web laying mechanism of the carding machine or a cross-laying machine. The web laying method is selected according to the strength requirements of the nonwoven fabric: for conventional strength requirements, parallel web laying is selected, where the fibers are arranged in the same direction, resulting in high longitudinal strength; for both longitudinal and transverse strength requirements, cross-laying is selected, where the fibers are arranged in a cross pattern, resulting in uniform longitudinal and transverse strength.

[0067] The weight of the fiber web is strictly controlled at 25g / m². 2 -100g / m 2 The specific weight is adjusted according to the application scenario of the nonwoven fabric, and the adaptation logic is as follows.

[0068] Thin nonwoven fabrics. Such as the surface layer of hygiene products and thin filter materials: 25-40 g / m². 2 The fiber web should be thin, uniform, and breathable. The laying speed should be controlled at 15-20m / min to ensure uniform thickness.

[0069] Medium-weight nonwoven fabrics, such as medical dressings and general packaging materials: 40-60 g / m² 2 It is required to balance strength and feel, and the net laying speed should be controlled at 10-15m / min.

[0070] Thick nonwoven fabrics, such as industrial filter materials and heavy-duty packaging materials: 60-100 g / m² 2 It requires high strength and structural stability. The mesh laying speed should be controlled at 5-10m / min. Multi-layer mesh laying can be used to ensure uniform thickness.

[0071] After the fiber web is laid and formed, the quality of the fiber web needs to be tested. The core test indicators include: thickness uniformity, no holes, no lumps, and consistent fiber distribution density. Unqualified fiber webs need to be combed and laid again.

[0072] Step 4: Latex Application: Anionic acrylic latex is evenly applied to the fiber mesh, ensuring full contact between the latex and the fibers, especially reacting with the cationic active groups on the surface of the cationic reinforced fibers. This lays the foundation for double cross-linking during the subsequent drying and baking process. Simultaneously, an appropriate application method must be selected based on the fiber mesh characteristics and product requirements to ensure uniform latex application and sufficient penetration, balancing strength and hand feel. After latex application, the fiber mesh conveying speed should be controlled at 5-20 m / min, and the conveying tension at 0.1-0.3 MPa to prevent fiber mesh stretching and deformation, ensuring uniform latex adhesion.

[0073] 4.1 Latex Preparation: Anionic acrylic latex is selected as the adhesive material. This latex is an acrylic copolymer emulsion with self-crosslinking function. Its molecular chain contains one or more anionic groups, such as carboxyl groups (-COOH) and sulfonic acid groups, which can undergo electrostatic attraction and chemical crosslinking reaction with the cationic groups on the surface of cationic reinforcing fibers. At the same time, the latex itself can undergo self-crosslinking to form a stable adhesive network.

[0074] The solid content of latex is strictly controlled between 15% and 50%. The adjustment of the solid content is directly related to the basis weight of the fiber web, and the adaptation logic is as follows.

[0075] Thin fiber web 25-40g / m 2 Use latex with a solid content of 15%-30%. Because the fiber web is thin and requires high breathability, low solid content latex can avoid the stiffness and reduced breathability caused by too much latex, while ensuring that the latex can penetrate evenly into the fiber web.

[0076] Thick fiber web 60-100g / m 2 Use latex with a solid content of 30%-50%. Due to the thicker fiber web and greater fiber quantity, high-solid-content latex provides sufficient bonding sites, ensuring adequate adhesion between fibers and avoiding insufficient adhesion that could lead to strength deficiencies. Fiber moisture content must be strictly controlled between 6%-10%. If the moisture content is >10%, dry it in 80℃ hot air for 10-15 minutes before pretreatment. The latex moisture content should match the solid content: 70%-85% for solid content of 15%-30%; 50%-70% for solid content of 30%-50%. The moisture content of the latex must be tested before use, with a deviation ≤±2%.

[0077] Before using the latex, it needs to be stirred evenly in an environment of 25℃±5℃ at a stirring speed of 200-300r / min for 10-15min to remove air bubbles in the latex. This will prevent air bubbles from forming during the application process, which could cause defects on the surface of the fiber mesh and affect the bonding effect.

[0078] 4.2 Application method: Based on the basis weight, thickness, air permeability requirements of the fiber web, and the application scenario of the product, select one of the following application methods to uniformly apply the anionic acrylic latex to the fiber web. Each application method must ensure that the latex is evenly distributed and fully penetrated. The specific operation is as follows.

[0079] (1) Impregnation method.

[0080] Applicable scenarios: Suitable for 40-100g / m³ 2 (Medium-thin and thick) fiber webs are used in applications requiring high bonding strength, such as industrial filter materials. Their core advantage lies in the ability of latex to fully penetrate the fiber web, encapsulating each fiber and forming a complete bond. The medium-thin type uses a low latex-to-fiber ratio (60%-70%) to avoid latex accumulation and ensure air permeability.

[0081] Specific operation: After the fiber web is laid and formed, it is completely immersed in anionic acrylic latex. The immersion time is controlled at 2-5 minutes, and adjusted according to the thickness of the fiber web: 2-3 minutes for thin fiber webs and 3-5 minutes for thick fiber webs. After immersion, the fiber web is sent to a rolling mill. The rolling rate is controlled at 60%-80%, and the rolling pressure is 0.3-0.5 MPa to remove excess latex, ensuring that there is no latex accumulation on the surface of the fiber web, and at the same time ensuring that the amount of latex penetrating into the fiber web is sufficient. After rolling, it is necessary to check whether the surface of the fiber web is uniform to avoid local situations where there is too much or too little latex.

[0082] (2) Spraying method.

[0083] Applicable scenarios: Thin and medium-thick fiber meshes, scenarios with high requirements for breathability and hand feel, such as hygiene products and medical dressings. The core advantage is that the latex is applied evenly and the amount is easy to control, which can avoid the fiber mesh feeling stiff.

[0084] Specific operation: Use a low-pressure spray device or a uniform spray device to atomize the well-stirred latex, controlling the atomized particle size to 10-50μm, with an appropriate compatibility of 25-30g / m³. 2 Fiber web, 10-20μm; 30-40g / m 2 Fiber web, 20-30μm; 40g / m 2 Above this, 30-50μm; then spray evenly onto the surface of the fiber web, controlling the spraying rate to 10-30g / m. 2 Adjust according to the weight of the fiber web: 10-20 g / m² for thin fiber web spraying. 2 Medium-thickness fiber mesh spraying: 20-30g / m 2During the spraying process, the distance between the spraying device and the fiber web should be controlled at 30-50cm, and the spraying speed should be synchronized with the fiber web conveying speed, such as 5-20m / min, to ensure that the latex is evenly distributed on the surface of the fiber web without any missed spraying or double spraying. After spraying, hot air pre-blowing can be used at a temperature of 80-100℃ and a wind speed of 2-3m / s to remove some of the moisture in the latex and prevent the latex from flowing.

[0085] (3) Foam impregnation method.

[0086] Applicable scenarios: Fiber webs of various weights, especially suitable for scenarios with high requirements for energy saving and soft hand feel, such as high-end hygiene products and medical dressings. The core advantages are low latex usage, uniform penetration, soft hand feel of the fiber web, and energy saving and consumption reduction.

[0087] Specific operation: First, mix anionic acrylic latex with a foaming agent at a mass ratio of 100:1-3, preferably sodium dodecyl sulfate (SDS), which has good foaming effect and excellent compatibility with latex; then, foam using foaming equipment, controlling the foam ratio at 5-10 times. The compatibility logic is as follows: latex solid content 15%-20%, foam ratio 8-10 times; solid content 20%-30%, foam ratio 6-8 times; solid content above 30%, foam ratio 5-6 times; foam density controlled at 0.1-0.2 g / cm³. 3 First, ensure that the foam is uniform and stable, with no obvious defoaming. Then, use a foam coating device to evenly coat the foam onto the surface of the fiber web, with the liquid carry-over rate controlled at 70%-80%. The liquid carry-over rate is the ratio of the mass of latex absorbed by the fiber web to the mass of the fiber web. After coating, let it stand for 1-2 minutes to allow the foam to naturally break down and the latex to evenly penetrate into the fiber web and encapsulate the fibers.

[0088] (4) Slot coating / slit coating method.

[0089] Applicable scenarios: Suitable for 50-100g / m³ 2 (Medium-thickness and thickness) fiber meshes are used in applications requiring extremely high strength, such as heavy-duty packaging materials and industrial protective materials. Their core advantage is the uniform latex coating and controllable thickness, which can form a uniform adhesive layer on the surface of the fiber mesh, significantly improving its strength.

[0090] Specific operation: Use a scraper or slit-type coating head to evenly coat the upper and lower surfaces of the fiber mesh with anionic acrylic latex of 30%-50% solids content. The coating thickness should be controlled at 0.1-0.2mm, adjusted according to the thickness of the fiber mesh: 0.15-0.2mm for thick fiber mesh and 0.1-0.15mm for medium-thick fiber mesh. During the coating process, control the coating speed to be synchronized with the fiber mesh conveying speed, such as 5-10m / min, to ensure uniform coating thickness and no scratches or missed coating. After coating, check the latex layer on the surface of the fiber mesh to ensure there are no bubbles or accumulations.

[0091] 4.3 Assisted Optimization: For scenarios that require further improvement in adhesion uniformity and polymerization efficiency, such as high-end products and products with high strength requirements, ultrasonic-assisted polymerization technology is introduced during the latex application process. The interaction between latex and fiber is optimized through the action of ultrasound. The specific parameters and principles are as follows.

[0092] Ultrasonic parameter control: frequency 20-40kHz, power 500-1000W, the ultrasonic device and the latex application device work synchronously, and the distance between the ultrasonic probe and the fiber web is 10-20cm to ensure that the ultrasonic waves can act evenly on the fiber web and latex.

[0093] By utilizing the cavitation effect and mechanical vibration of ultrasound, the acrylate monomers in the latex are uniformly dispersed, reducing latex agglomeration. At the same time, the reaction rate between the latex and the surface active groups of the cationic reinforcing fibers is accelerated, ensuring that the latex can fully contact and combine with each fiber. This provides a guarantee for the double crosslinking in the subsequent drying and baking process, and ultimately further improves the strength uniformity and overall strength of the nonwoven fabric.

[0094] Step 5: Drying and baking treatment: By controlling the temperature and time, a dual cross-linking reaction is achieved, which involves the self-cross-linking of latex and the cross-linking of latex with cationic reinforcing fibers. This constructs a stable adhesive network that tightly connects the fibers, significantly improving the dry and wet strength of the nonwoven fabric. At the same time, reasonable parameter control prevents fiber damage and latex decomposition, ensuring stable product performance.

[0095] 5.1 Processing equipment: The fiber web with latex applied is fed into the drying and baking equipment. The equipment is selected according to the production scale and product requirements, including: drying oven, hot air penetration dryer, multi-temperature zone drying equipment, etc.

[0096] The preferred treatment method combines hot air drying and hot rolling. Hot air drying removes moisture from the latex, allowing it to gradually cross-link. Hot rolling further strengthens the adhesion between fibers, ensuring a complete cross-linking reaction and resulting in a denser nonwoven fabric structure, improving strength and dimensional stability. Applications that omit hot rolling include: latex solids content ≤30%, fiber web basis weight ≤40g / m². 2 Furthermore, if the surface flatness requirement is not high, hot air drying can be used; if the latex solid content is ≤30% but the fiber web basis weight is >40g / m², then... 2 Cross-laid mesh + hot air penetration drying can be used to ensure tight bonding between fibers.

[0097] 5.2 Parameter Control: The total temperature of drying and baking is controlled between 120℃ and 180℃, and the total time is controlled between 3 and 20 minutes. The specific parameters are flexibly adjusted according to the latex solid content and fiber web weight. The principle is to use low temperature and long time for low solid content and thin fiber web, and high temperature and short time for high solid content and thick fiber web, so as to avoid problems such as insufficient cross-linking of latex, fiber damage and latex decomposition. The specific grouping parameters are as follows.

[0098] (1) Low solid content, thin fiber web.

[0099] Applicable conditions: latex solid content 15%-30%, fiber web weight 25-40 g / m² 2 .

[0100] Parameter control: Temperature 120℃-145℃, time 6-20 minutes; latex solid content 15%-20%, fiber web basis weight 25-30g / m². 2 Select a temperature of 120℃-130℃ and a time of 15-20 minutes to ensure slow cross-linking of the latex and avoid rapid evaporation of moisture, which would cause the latex surface to form a skin while the interior remains uncross-linked; the latex solid content should be 20%-30%, and the fiber web basis weight should be 30-40 g / m². 2 The temperature is selected as 130℃-145℃, and the time is 6-15 minutes, which takes into account both drying efficiency and cross-linking effect.

[0101] (2) High solids content, thick fiber web.

[0102] Applicable conditions: latex solid content 30%-50%, fiber web weight 60-100g / m² 2 .

[0103] Parameter control: Temperature 150℃-180℃, time 3-10 minutes; latex solid content 30%-40%, fiber web basis weight 60-80g / m². 2 For latex solids content of 40%-50% and fiber web basis weight of 80-100g / m2, select a temperature of 165℃-180℃ and a time of 3-5 minutes to ensure rapid cross-linking of the latex while avoiding yellowing and brittleness of the fibers due to prolonged high-temperature treatment.

[0104] (3) Multi-temperature zone treatment.

[0105] Applicable scenarios: High-end products and scenarios with high requirements for strength uniformity. It can effectively avoid local overheating that could damage the fibers and ensure that the cross-linking reaction is sufficient and uniform.

[0106] Parameter control: A multi-temperature zone drying device is used, with the temperature gradually increased from 130℃ to 150℃-170℃, divided into 3-4 temperature zones. The temperature gradient of each zone is 10-20℃, and the total processing time is 7-15 minutes. For example, the first temperature zone is 130℃ for 2-3 minutes to remove surface moisture; the second temperature zone is 140℃-150℃ for 3-5 minutes for initial cross-linking; and the third temperature zone is 150℃-170℃ for 2-7 minutes for full cross-linking. By gradually increasing the temperature, the latex slowly cross-links, forming a stable adhesive network while protecting the fibers from damage.

[0107] In addition, the hot rolling parameters must match the drying and baking parameters. The hot rolling temperature should be controlled at 140℃-170℃, and the hot rolling pressure should be 0.4-0.8MPa. The applicable logic is as follows: high heat-resistant fibers (aramid, polyester), temperature 160-170℃, pressure 0.6-0.8MPa; medium heat-resistant fibers (polypropylene, ES fiber), temperature 150-160℃, pressure 0.5-0.6MPa; poor heat-resistant fibers (viscose, lyocell, cotton), temperature 140-150℃, pressure 0.4-0.5MPa. The difference between the drying temperature and the hot rolling temperature should be controlled at 10-20℃ to ensure sufficient cross-linking. The hot rolling speed should be synchronized with the fiber web conveying speed, 5-20m / min, to ensure tight adhesion between fibers and improve the strength and surface smoothness of the nonwoven fabric.

[0108] 5.3 Reaction Mechanism: During the drying and baking process, a double cross-linking reaction occurs simultaneously. This is the core principle behind the significant improvement in the strength of the nonwoven fabric of this invention. The double cross-linking reaction works synergistically to construct a stable structure of latex interpenetrating network and cation bridging. The specific reaction mechanism is as follows.

[0109] (1) First cross-linking, latex self-cross-linking reaction: Under the action of drying and baking temperature, the active groups (such as acrylate groups) on the molecular chain of anionic acrylic latex undergo self-cross-linking reaction to form a stable latex interpenetrating network; this network can tightly wrap each fiber in the fiber web, fill the gaps between fibers, strengthen the basic adhesion between fibers, form the basic strength skeleton of nonwoven fabric, and prevent the fibers from loosening and falling off.

[0110] (2) Second cross-linking, ionic bonding and chemical cross-linking reaction: As drying and baking proceed, the anionic groups (-COOH, -SO3H, etc.) on the latex molecular chain interact specifically with the cationic active groups (-NH3⁺, quaternary ammonium salt groups, etc.) on the surface of the cationic reinforcing fiber (chitosan fiber), first forming electrostatic attraction (ionic bonding), so that the latex and the cationic reinforcing fiber are tightly bound together; then, under the action of high temperature, some anionic groups and cationic groups further undergo chemical cross-linking reaction, including but not limited to amidation reaction, such as -COOH reacting with -NH3+ to form amide bond, ionic polymerization reaction, so that the latex and the cationic reinforcing fiber form an irreversible and stable bond. In the dual crosslinking reaction, ionic bonding is the basic adhesive effect, while chemical crosslinking is the reinforcing adhesive effect. Together, they form a three-dimensional "latex-fiber" adhesive network. Ionic bonding ensures initial connection between fibers, while chemical crosslinking enhances adhesive stability. Ionic bonding remains stable even in humid environments; therefore, in some embodiments (such as Examples 3 and 5), the wet strength improvement is significantly higher than in the dry state. Traditional nonwoven fabrics, however, rely solely on latex self-crosslinking, and the latex network softens easily in humid environments, resulting in poor wet strength. The specific reaction conditions for chemical crosslinking are also clearly defined: the amidation reaction requires temperatures above 140°C and a reaction time of at least 3 minutes; ionic bonding preferentially occurs at 120-145°C; and chemical crosslinking is accelerated above 150°C. Latex self-crosslinking and ionic bonding occur simultaneously, mutually promoting the formation of the adhesive network.

[0111] Step 6: Post-processing.

[0112] 6.1 Cooling and shaping: The dried and baked nonwoven fabric is sent to a cooling device to cool to room temperature (25℃±5℃) to avoid residual heat causing the nonwoven fabric to shrink and deform, and to ensure dimensional stability.

[0113] 6.2 Edge trimming and winding: According to the product specifications, the non-woven fabric is trimmed by an edge trimming machine to remove irregular parts of the edges. Then, it is wound by a winding device. The winding speed is controlled at 10-20m / min to ensure that the winding is flat and wrinkle-free.

[0114] 6.3 Inspection and Packaging: The wound nonwoven fabric undergoes quality inspection, testing its dry strength, wet strength, transverse strength, and thickness uniformity. Defective products are rejected, and qualified products are packaged, sealed, and stored to prevent moisture from affecting performance. Product quality acceptance standards: ① Strength: Dry longitudinal strength ≥ 100 N / sCM (thin type 25-40 g / m²) 2 ≥200N / SCM (medium-thickness type 40-60g / m²) 2 ≥300N / SCM (thick type 60-100g / m²) 2); Dry transverse strength ≥15N / SCM (thin type), ≥30N / SCM (medium-thick type), ≥60N / SCM (thick type); Wet longitudinal strength ≥60N / SCM (thin type), ≥120N / SCM (medium-thick type), ≥180N / SCM (thick type); Wet transverse strength ≥8N / SCM (thin type), ≥18N / SCM (medium-thick type), ≥36N / SCM (thick type); ② Thickness uniformity: thickness deviation ≤±5%; ③ Appearance: no holes, no lumps, no latex accumulation, neat edges; ④ Mixing uniformity: cationic fiber ratio deviation ≤±0.2%; All test results of the examples must meet this standard. Unqualified products must be reworked according to the process tolerance measures. Specific rework process: Products that do not meet the strength standard need to be dried and baked again (parameters adjusted according to the corresponding specifications). Products that do not meet the appearance and mixing uniformity standards need to be disassembled and re-opened and mixed and subsequent processes. After rework, all indicators need to be retested until they meet the standard.

[0115] The following 10 specific embodiments further illustrate the specific implementation details of this preparation method and verify its strength improvement effect. Each embodiment is only used to explain the present invention and does not limit the scope of protection of the present invention.

[0116] Example 1.

[0117] 1. Raw materials and proportions: The main fiber is polyester staple fiber 1.5D×38mm, accounting for 95% of the total fiber weight; the cationic reinforcing fiber is chitosan fiber 1.2D×38mm, with a deacetylation degree of 95%, accounting for 5% of the total fiber weight; the anionic acrylic latex has a solid content of 40% and contains carboxyl groups.

[0118] 2. Preparation process.

[0119] (1) Pretreatment: pre-open the polyester staple fiber and chitosan fiber separately to remove impurities.

[0120] (2) Opening and mixing: The above polyester staple fiber and chitosan fiber are opened by an opening machine at a speed of 1000 r / min for 10 min, and then put into a mixing box for mixing at a speed of 400 r / min for 15 min.

[0121] (3) Carding into a web: The mixed fiber raw materials are carded by a carding machine at a speed of 2000 r / min and a spacing of 0.2 mm to form a web with a basis weight of 40 g / m². 2 Fiber web.

[0122] (4) Latex application: Anionic acrylic latex is applied to the fiber web by impregnation, with the liquid roll-off rate controlled at 80%. Impregnation time is 3 minutes.

[0123] (5) Drying and baking: The fiber web with latex applied is conveyed to the drying oven and dried and hot rolled at 160°C for 3 minutes.

[0124] (6) Post-processing: After cooling to room temperature, trimming and winding, a chemically bonded nonwoven fabric with improved strength is obtained. Inspection and packaging.

[0125] 3. Product performance: The dry longitudinal strength of the nonwoven fabric is 363.3 N / SCM, and the transverse strength is 59.0 N / SCM, which is significantly higher than similar products on the market.

[0126] Reference Figure 11 A magnified image of a nonwoven fabric sample containing 5% chitosan fiber shows that the acrylic latex is evenly connected to the fiber, resulting in high pore size uniformity.

[0127] Example 2.

[0128] 1. Raw materials and proportions: The main fiber is cotton fiber, accounting for 85% of the total fiber weight; the cationic reinforcing fiber is carboxymethyl chitosan fiber, 2.0D×40mm, with a degree of deacetylation of 60%, accounting for 15% of the total fiber weight; the anionic acrylic latex has a solid content of 30% and contains sulfonic acid groups.

[0129] 2. Preparation process.

[0130] (1) Pretreatment: pre-opened cotton fibers and carboxymethyl chitosan fibers.

[0131] (2) Opening and mixing: The cotton fiber and carboxymethyl chitosan fiber are thoroughly mixed by mechanical opening and airflow mixing at a speed of 900 r / min for 12 min.

[0132] (3) Carding and web formation: The mixed fibers are carded and web-formed using a cross-laying machine to form a web with a basis weight of 60 g / m². 2 Fiber web.

[0133] (4) Latex application: Apply anionic acrylic latex (solid content of 30%) to the surface of the fiber mesh using a uniform spraying device, with a spraying amount of 20g / m. 2 .

[0134] (5) Drying and baking: The fiber web is dried at 145°C using a hot air penetration dryer for 5 minutes.

[0135] (6) Post-processing: After drying and baking, the product is naturally cooled and rolled up to obtain the final product. Inspection and packaging.

[0136] 3. Product effect: The non-woven fabric is soft to the touch and breathable. The dry transverse strength is 45.2 N / SCM and the wet transverse strength is 15.1 N / SCM, showing a significant improvement in strength.

[0137] Example 3.

[0138] 1. Raw materials and proportions: The main fiber is polypropylene fiber, 2.2D×51mm, accounting for 98% of the total fiber weight; the cationic reinforcing fiber is chitosan fiber, 1.8D×38mm, with a deacetylation degree of 80%, accounting for 2% of the total fiber weight; the anionic acrylic latex has a solid content of 20% and contains carboxyl and sulfonic acid groups.

[0139] 2. Preparation process.

[0140] (1) Pretreatment: Gently loosen chitosan fibers and pre-loosen polypropylene fibers.

[0141] (2) Opening and mixing: After opening the polypropylene fiber and chitosan fiber separately, the speed is 800 r / min and the time is 8 min. Then, they are put into the cotton mixing curtain according to the proportion and mixed at 300 r / min for 20 min.

[0142] (3) Carding into a web: The mixed fibers are carded into a web with a basis weight of 25 g / m² using a high-speed carding machine. 2 A single-layer fiber web.

[0143] (4) Latex application: Anionic acrylic latex (solid content of 20%) is applied to the fiber mesh by foam impregnation, with a foam ratio of 8 times and a liquid carry-over rate of 70%.

[0144] (5) Drying and baking: The fiber web is sent into the drying room and dried and hot rolled at 120°C for 8 minutes to ensure that the cationic groups of chitosan fiber react fully.

[0145] (6) Post-processing: After processing, the rolls are wound into rolls, inspected and packaged.

[0146] 3. Product performance: Thin non-woven fabric with a dry transverse strength of 22.7 N / SCM and a wet transverse strength of 13.7 N / SCM, meeting the requirements of thinness and high strength for hygiene products.

[0147] Example 4.

[0148] Raw materials and proportions: Main fiber: ES fiber (core-sheath composite fiber, 3.0D×51mm), accounting for 90% of the total fiber weight. Cationic fiber: Hydroxybutyl chitosan fiber (50% deacetylation, 1.5D×38mm), accounting for 10% of the total fiber weight.

[0149] Preparation process.

[0150] 1. Opening and mixing: ES fiber and hydroxybutyl fiber are fully opened and mixed using a multi-compartment blending machine.

[0151] 2. Carding into web: A double-doff carding machine is used to form a thick fiber web with a basis weight of 80g / m².

[0152] 3. Latex application: Apply anionic acrylic latex (45% solid content) evenly to the upper and lower surfaces of the fiber mesh by scraping.

[0153] 4. Drying and baking: The coated fiber web is passed through the oven above the hot rolling mill and rapidly dried and hot rolled at a temperature of 180°C for 3 minutes.

[0154] 5. Post-processing: After drying, the product is calendered, cooled, rewound, inspected, and packaged.

[0155] Product performance: Dry longitudinal strength 420.5 N / SCM, transverse strength 85.3 N / SCM; wet longitudinal strength 260.2 N / SCM, transverse strength 48.7 N / SCM, meeting the standards for thick products.

[0156] Example 5.

[0157] Raw materials and proportions: Main fiber: viscose fiber (1.3D×38mm), accounting for 99% of the total fiber weight. Cationic fiber: hydroxypropyl chitosan fiber (average length 38mm, degree of deacetylation 45%), accounting for 1% of the total fiber weight.

[0158] Preparation process.

[0159] 1. Opening and Mixing: After gently opening the hydroxypropyl chitosan fibers, mix them with viscose fibers in a mixing box to avoid excessive damage to the hydroxypropyl fibers.

[0160] 2. Carding into a web: The web is formed by a carding machine into a thin fiber web with a weight of 30g / m².

[0161] 3. Latex application: The diluted anionic acrylic latex (solid content of 15%) is atomized and sprayed onto the surface of the fiber mesh using a low-pressure spray method.

[0162] 4. Drying and baking: Place the fiber web in a circulating hot air oven and gently dry and bake it at 125℃ for about 6 minutes.

[0163] 5. Post-processing: After cooling, a soft and high-strength nonwoven fabric is obtained.

[0164] Product performance: Dry longitudinal strength 120.3 N / SCM, transverse strength 18.5 N / SCM; wet longitudinal strength 75.6 N / SCM, transverse strength 9.8 N / SCM, meeting the standards for thin products.

[0165] Example 6.

[0166] Raw materials and proportions: Main fiber: Aramid 1414 chopped strand fiber (2.0D×51mm), accounting for 92% of the total fiber weight. Cationic fiber: Quaternary ammonium salt chitosan fiber (2.0D×51mm, degree of deacetylation 40%), accounting for 8% of the total fiber weight.

[0167] Preparation process.

[0168] 1. Opening and mixing: Quaternary ammonium salt chitosan fibers are opened and grasped multiple times to achieve uniform mixing.

[0169] 2. Carding into a web: Using a heavy-duty carding machine, a high-strength fiber web with a basis weight of 100g / m² is formed.

[0170] 3. Latex application: The impregnation process is adopted to fully impregnate the fiber web with anionic acrylic latex (solid content of 50%), with a roll-off rate of 60%.

[0171] 4. Drying and baking: Drying and baking are carried out at a high temperature of 170℃ for 4 minutes to ensure a strong bond is formed on the surface of the high-performance fiber.

[0172] 5. Post-processing: The processed materials are cut and packaged.

[0173] Product performance: Dry state: 580.7 N / SCM longitudinally and 120.5 N / SCM laterally; Wet state: 320.3 N / SCM longitudinally and 72.8 N / SCM laterally; suitable for industrial protection scenarios.

[0174] Example 7.

[0175] Raw materials and proportions: Main fiber: Lyocell fiber (1.4D×38mm), accounting for 80% of the total fiber weight. Cationic fiber: Carboxymethyl chitosan fiber (1.5D×38mm, 45% deacetylation), accounting for 20% of the total fiber weight (maximum proportion). Anionic acrylic latex (48% solids content, containing carboxyl groups).

[0176] Preparation process.

[0177] 1. Opening and Mixing: After pre-opening the Lyocell fiber and carboxymethyl chitosan fiber, a weighing-type automatic mixing system is used for precise proportioning and mixing.

[0178] 2. Combing into a web: A precision combing machine is used to form a fiber web with a weight of 50g / m² and extremely high uniformity.

[0179] 3. Latex Application: A slit-type coating head is used to precisely apply a high-concentration anionic acrylic latex (48% solids content) to the surface of the fiber web. Ultrasonic-assisted polymerization technology is utilized during latex application. The cavitation effect and mechanical vibration of ultrasound promote uniform dispersion of monomers in the latex, reduce agglomeration, and accelerate the polymerization reaction, thereby improving polymerization efficiency and adhesion uniformity.

[0180] 4. Drying and baking: The fiber web is passed through a multi-temperature drying device, with the temperature gradually increased from 130℃ to 150℃, and the total processing time is 7 minutes to ensure that the reaction is complete.

[0181] 5. Post-processing: The final product is rolled up after inspection.

[0182] Product performance: Dry state: 280.5 N / scm longitudinally and 42.3 N / scm transversely; Wet state: 160.7 N / scm longitudinally and 22.8 N / scm transversely; suitable for high-end medical dressings.

[0183] Example 8: Refer to Figure 2 and Figure 3 .

[0184] Raw materials and proportions: Main fiber: Lyocell fiber (1.4D×38mm), accounting for 95% of the total fiber weight; Cationic fiber: Carboxymethyl chitosan fiber (1.5D×38mm, 45% deacetylation), accounting for 5% of the total fiber weight.

[0185] Preparation process.

[0186] 1. Opening and Mixing: After pre-opening the Lyocell fiber and carboxymethyl chitosan fiber, a weighing-type automatic mixing system is used for precise proportioning and mixing.

[0187] 2. Combing into a web: A fiber web with different weight ratios and extremely high uniformity is formed through a precision combing machine.

[0188] 3. Latex application: Using a slit-type coating head, a high concentration of anionic acrylic latex (solid content of 48%) is precisely applied to the surface of the fiber web.

[0189] 4. Drying and baking: The fiber web is passed through a multi-temperature zone drying device, with the temperature gradually increased from 130℃ to 150℃, and the total processing time is 10 minutes to ensure that the reaction is complete.

[0190] 5. Post-processing: The final product is rolled up after inspection.

[0191] Product performance: Dry state: 150.8 N / scm longitudinally and 25.6 N / scm transversely; Wet state: 90.5 N / scm longitudinally and 11.3 N / scm transversely; suitable for the surface of hygiene products.

[0192] The above implementation scheme and the commercially available 40 g / m² chemically bonded nonwoven fabric were tested for tensile strength using the following method.

[0193] Take a test sample approximately 1 meter long. The test sample should be free of obvious defects and wrinkles. Cut 5 samples along the length and 5 samples along the width. Each sample should be 100 mm from the edge (adjust the distance to the edge if the size is too small), and evenly distributed along the length and width of the sample. Each sample should be 50 mm ± 0.5 mm wide and 200 mm long. Fix the samples to the tensile testing machine fixtures, with a distance of 200 mm ± 1 mm between the fixtures. Straighten the sample and test at a constant speed of 100 mm / min. Record the force-elongation curve for each sample.

[0194] Discard any specimen that fractures at the fixture or has at least one point of fracture at the fixture.

[0195] Report the average fracture strength in the length and width directions separately, and summarize the experimental results, see [link to report]. Figure 3 .

[0196] Due to the addition of cationic fibers, the average breaking strength of the nonwoven fabric samples was greatly improved. Even the sample with a weight of 30 grams per square meter had similar strength measurement data to the commercially available sample with a weight of 40 grams per square meter that did not contain cationic fibers.

[0197] Example 9.

[0198] Reference Figure 4 and Figure 5 Raw materials and proportions: Based on the fact that the main fiber is viscose fiber (1.3D×38mm) and the cationic fiber is chitosan fiber (1.5D, average length 55mm, degree of deacetylation 90%), experimental groups were designed according to different proportions of the main fiber to the total fiber weight.

[0199] Preparation process.

[0200] 1. Opening and mixing: After opening the chitosan fibers and viscose fibers separately, they are mixed in a mixing box.

[0201] 2. Carding into a web: The web is formed by a carding machine into a thin fiber web with a standard weight of 35g / m².

[0202] 3. Latex application: Using a foam coating method, the anionic acrylic latex (solid content of 50%) mixed with foaming agent (SDS) is foamed and then evenly coated onto the surface of the fiber web.

[0203] 4. Drying and baking: The fiber web is placed in a circulating hot air oven and dried and baked at a temperature of 125℃ for about 8 minutes.

[0204] 5. Post-processing: After cooling, a soft and high-strength nonwoven fabric is obtained.

[0205] Testing: Lateral tensile strength test: Take a test sample of approximately 1 meter from the material. The test sample should be free of obvious defects and wrinkles. Cut 5 samples in the width direction, each sample should be 100mm from the edge (adjust the distance from the edge appropriately for samples that are too small), and evenly distributed along the length and width of the sample. Each sample should be 50mm ± 0.5mm wide and 200mm long. Fix the samples to the tensile testing machine fixtures, with a distance of 200mm ± 1mm ​​between the fixtures. Straighten the sample and test at a constant speed of 100mm / minute. Record the force-elongation curve for each sample.

[0206] Discard any specimen that fractures at the fixture or has at least one point of fracture at the fixture.

[0207] Wet strength test: Immerse the sample in a solution containing 1g of nonionic surfactant per liter of distilled water for at least 1 hour, remove it, shake off excess water, and immediately test it using the transverse strength test method.

[0208] Test results.

[0209] Results from different experimental groups showed that the introduction of cationic fibers, represented by chitosan fibers, had a positive impact on the transverse tensile strength of the product. This indicates that the ionic bonding / chemical cross-linking between latex and cationic fibers strengthens the cross-linking effect of the latex itself, enhancing the internal structural stability of the nonwoven fabric and the bonding force between fibers. The results showed that the introduction of 2.5% chitosan could increase the transverse tensile strength under dry conditions by 22.9%, while the effect on the transverse tensile strength under wet conditions was even more significant, reaching 81.2%. This demonstrates that the introduction of cationic fibers can significantly improve product performance. Further increasing the use of cationic fibers did not significantly increase the benefit, possibly because the reaction of a large amount of cationic fibers with acrylic latex led to a decrease in the self-cross-linking ratio of the latex. This can be corrected by adjusting the amount of adhesive used.

[0210] Example 10: Refer to Figure 6 , Figure 7 , Figure 8 , Figure 9 and Figure 10 .

[0211] Raw materials and proportions: Based on the fact that the main fiber is lyocell fiber (1.3D×38mm) and the cationic fiber is chitosan fiber (1.5D, average length 55mm, degree of deacetylation 90%), experimental groups were designed according to different proportions of the main fiber to the total fiber weight.

[0212] Preparation process.

[0213] 1. Opening and mixing: After opening the chitosan fibers and lyocell fibers separately, they are mixed in a mixing box.

[0214] 2. Carding and web formation: The web is formed by a carding machine with a weight of 38g / m². 2 Standard thin fiber web.

[0215] 3. Latex application: Using a foam coating method, the anionic acrylic latex (solid content of 50%) mixed with foaming agent (SDS) is foamed and then evenly coated on the surface of the fiber web.

[0216] 4. Drying and baking: Place the fiber web in a circulating hot air oven and gently dry and bake it at 125°C for about 8 minutes.

[0217] 5. Post-processing: After cooling, a soft and high-strength nonwoven fabric is obtained.

[0218] Testing.

[0219] Lateral tensile strength test: Take a test sample of approximately 1 meter from the material. The test sample should be free of obvious defects and wrinkles. Cut 5 samples in the width direction, each sample should be 100mm from the edge (adjust the distance from the edge appropriately for samples that are too small), and evenly distributed along the length and width of the specimen. Each sample should be 50mm ± 0.5mm wide and 200mm long. Fix the samples to the tensile testing machine fixtures, with a distance of 200mm ± 1mm ​​between the fixtures. Straighten the specimen and test at a constant speed of 100mm / minute. Record the force-elongation curve for each specimen.

[0220] Test results are shown Figures 7-10 .

[0221] The experimental results showed that the introduction of cationic fibers, represented by chitosan fibers, had a positive impact on the transverse tensile strength of the product. The ionic bonding / chemical cross-linking between the latex and the cationic fibers enhanced the cross-linking effect of the latex itself, thereby improving the internal structural stability of the nonwoven fabric and the bonding force between fibers. The results showed that the introduction of 2.5% chitosan resulted in a 31.5% increase in transverse tensile strength under dry conditions when the basis weight was increased to 38 GSM. This demonstrates that the introduction of cationic fibers can stably improve product performance.

[0222] The above 10 embodiments cover different types of main fibers, cationic reinforcing fibers, mixing ratios, fiber web basis weights, and latex application methods. All embodiments avoid problems such as raw material compatibility, uneven dispersion, and insufficient cross-linking by optimizing process parameters. The product strength meets the acceptance standards for the corresponding types of nonwoven fabrics, verifying the versatility and effectiveness of this preparation method. Process parameters can be flexibly adjusted according to actual application scenarios to achieve the core goal of strength improvement. The residual antistatic agent content in all embodiments is ≤0.05%, meeting the safety standards for medical and hygiene products; the batch-to-batch product strength deviation is ≤±5%, indicating good stability.

[0223] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing nonwoven fabric using a chemical bonding method that enhances strength with chitosan, characterized in that, Includes the following steps: Prepare fiber raw materials consisting of main fibers and chitosan fibers, with the main fibers accounting for 80%-99.5% of the total weight of the fiber raw materials; the degree of deacetylation of the chitosan fibers is 40%-95%. After the main fibers and chitosan fibers are opened separately, they are mixed evenly and combed to form a uniform fiber web. Anionic acrylic latex is applied to the fiber web; the fiber web is dried and hot-rolled to make the latex self-crosslink and its anionic groups form a dual crosslinking structure of ionic bonding and chemical crosslinking with the cationic active groups of chitosan fibers; After cooling, trimming, and winding, nonwoven fabric is obtained.

2. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 1, characterized in that: The chitosan fiber is one of the following: quaternary ammonium salt modified chitosan fiber, hydroxylated modified chitosan fiber, or carboxymethyl chitosan fiber with cationic activity. The main fiber is any one or more of the following: cellulose fiber, modified cellulose fiber, polyester fiber, ES fiber, PBS fiber, PLA fiber, polyester staple fiber, cotton fiber, polypropylene fiber, viscose fiber, aramid 1414 chopped fiber, and lyocell fiber.

3. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 1, characterized in that: The chitosan fiber is incorporated at a ratio of 2.5% to 8% of the total weight of the fiber raw materials.

4. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 1, characterized in that: The solid content of the anionic acrylic latex is 15%-50%.

5. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 1, characterized in that: The drying and hot rolling processes are carried out at temperatures of 120°C-180°C for 3-20 minutes.

6. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 1, characterized in that: The nonwoven fabric has a dual cross-linking structure formed by latex self-cross-linking and latex-chitosan fiber ionic bonding / chemical cross-linking, with a dry transverse strength ≥20.3 N / SCM and a wet transverse strength ≥13.7 N / SCM.

7. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 1, characterized in that: During the process of applying anionic acrylic latex to the fiber web, ultrasonic-assisted polymerization technology is used. The ultrasonic frequency is controlled at 20-40kHz and the power is 500-1000W to promote the uniform dispersion of acrylate monomers in the anionic acrylic latex and accelerate the reaction between the latex and chitosan fibers.

8. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 1, characterized in that: The pressure of hot rolling is controlled at 0.4-0.8 MPa, the hot rolling speed is synchronized with the fiber web conveying speed, and the difference between the drying temperature and the hot rolling temperature is controlled at 10-20℃ to ensure that the double cross-linking reaction is fully carried out.

9. The method for preparing nonwoven fabric using chitosan-enhanced chemical bonding according to claim 8, characterized in that: The hot rolling temperature parameters are adjusted according to the latex solid content and fiber web basis weight, and the hot rolling temperature is controlled between 140℃ and 170℃. The drying and hot rolling treatment adopts a combination of hot air drying and hot rolling. The hot rolling temperature is 140℃-150℃ for the main fibers with poor heat resistance and 160℃-170℃ for the main fibers with strong heat resistance.

10. A nonwoven fabric based on the chemical bonding method using chitosan to enhance strength according to claim 1 or 2, characterized in that: The fiber raw material includes chitosan fiber.

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