A process for sealing the edges of nonwoven fabric bags against cracking

Abstract

The present application relates to the technical field of non-woven fabric product processing, in particular to a crack-proof non-woven fabric bag edge sealing process, which comprises the following steps: edge pretreatment, surface activation after cleaning and impurity removal, humidity regulation and hot melt toughening glue layer coating; edge folding preforming and reinforcement embedding, cold pressure preforming after folding the edge and embedding the reinforcing fiber silk; gradient composite welding sealing, sequentially performing low-temperature pre-melting, medium-frequency welding, high-temperature shaping fusion; gradient cooling shaping, three-stage cooling and full-range pressure maintaining; post-sealing toughening treatment, secondary surface toughening treatment on the sealed edge, and sealing processing is completed. Through multi-process synergistic optimization, the process improves the edge sealing binding force and toughness, avoids virtual welding, delamination and stress cracking, balances the welding strength and stability, is suitable for large-scale production, solves the pain point of easy cracking of the sealed edge, and prolongs the service life of the non-woven fabric bag.

Description

Technical Field

[0001] This invention relates to the field of nonwoven fabric processing technology, specifically to an edge sealing process for anti-cracking nonwoven bags. Background Technology

[0002] With the continuous advancement of environmental protection policies, non-woven bags, as biodegradable and reusable environmentally friendly packaging products, have widely replaced traditional plastic packaging bags and are used in various fields such as retail, supermarkets, warehousing and logistics, and gift packaging. Edge sealing is the core process in the processing of non-woven bags. The structural stability of the sealing directly determines the load-bearing capacity, service life, and safety of the non-woven bag, while edge cracking is the most common failure mode of non-woven bags during use.

[0003] Currently, the mainstream edge sealing methods for nonwoven bags are single hot-press welding or ultrasonic welding. Both methods have significant technical drawbacks in practical applications. The single hot-press welding process achieves the melting and bonding of nonwoven fibers through high-temperature hot pressing. The process is simple to operate, but it requires extremely high precision in temperature and pressure control. If the temperature is too low, insufficient welding and insufficient peel strength may occur. If the temperature is too high, the nonwoven fibers will become brittle due to over-melting, and the edge sealing toughness will decrease significantly, making it prone to cracking when bent or under heavy load. At the same time, the conventional hot-press process can only achieve surface fiber welding, resulting in uneven bonding force inside the edge sealing, which can easily lead to delamination and cracking after long-term use.

[0004] While ultrasonic welding offers high welding efficiency, it is extremely sensitive to the weight, moisture content, and surface cleanliness of the nonwoven fabric substrate. This makes it prone to problems such as incomplete welds, missed welds, and edge damage, resulting in poor batch production stability. Furthermore, stress concentration at the weld points makes them highly susceptible to breakage after repeated bending and tensile stress. Existing improved processes often enhance edge sealing strength through simple adhesive application and single-layer folding, but these suffer from poor compatibility between the adhesive layer and the nonwoven fabric substrate, leading to delamination after thermal cycling. The folded edge structure also fails to effectively distribute stress, thus not fundamentally solving the problem of edge cracking. In addition, existing sealing processes often employ rapid cooling for shaping, which can generate significant internal stress within the seal. This stress gradually releases during storage or use, causing edge warping and brittleness. This approach fails to balance weld strength and flexural toughness, severely limiting the widespread application of nonwoven bags in high-load, reusable scenarios. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a crack-resistant nonwoven bag edge sealing process.

[0006] (II) Technical Solution A crack-resistant nonwoven bag edge sealing process includes the following steps: S1 Edge Pretreatment: The edges of the nonwoven bag blank to be sealed are cleaned and impurities are removed. After removing edge lint and stains, the edge area with a width of 10-20mm is surface activated by low-temperature plasma with a treatment power of 80-150W and a treatment time of 3-10s. After treatment, the humidity of the edge area is controlled to keep the moisture content of the edge nonwoven fabric stable at 0.8%-2.5%. At the same time, a hot melt toughening adhesive layer with a thickness of 0.02-0.08mm is uniformly coated on the bonding surface of the edge to be sealed to complete the edge pretreatment. S2 edge preforming and reinforcement embedding: The pre-treated bag edge is double-folded in reverse, with a fold width of 8-15mm. After folding, multiple parallel PP reinforcement fibers are evenly embedded between the two folded layers. The fiber diameter is 0.1-0.3mm and the spacing between adjacent fibers is 2-5mm. After embedding, the folded edge is cold-pressed and pre-shaped with a pressure of 0.2-0.4MPa for 2-5s to obtain the pre-formed edge sealing blank. S3 Gradient Composite Welding and Sealing: The pre-formed edge sealing blank undergoes a three-stage gradient welding process. First, a low-temperature pre-melting is performed using a hot press roller at 110-130℃, with a hot pressing pressure of 0.3-0.5MPa and a pre-melting time of 1-3s. Then, a medium-frequency welding is performed using an ultrasonic welding head at 20-35kHz, with a welding pressure of 0.4-0.6MPa and a welding time of 0.5-2s. Finally, a high-temperature shaping and fusion is performed using a hot press roller at 135-150℃, with a hot pressing pressure of 0.5-0.7MPa and a fusion time of 2-4s, completing the edge sealing welding. S4 Gradient Cooling and Shaping: The welded edge seal is subjected to three-stage gradient cooling. First, it is pre-cooled with warm air at 40-60℃ for 3-6 seconds, then cooled with cold air at 15-25℃ for 5-10 seconds, and finally cooled with low-temperature roller pressing at 5-10℃ for 2-4 seconds. Throughout the cooling process, a holding pressure of 0.1-0.2MPa is continuously applied to the edge seal. S5 edge sealing toughening treatment: After cooling and shaping, the edge sealing is subjected to a secondary surface toughening treatment with 60-100W low-temperature plasma for 2-6 seconds, finally completing the sealing process of the non-woven bag edge.

[0007] Preferably, in step S1, the low-temperature plasma treatment uses a mixture of argon and nitrogen as the working gas, wherein the volume percentage of argon in the mixture is 60%-80% and the volume percentage of nitrogen is 20%-40%.

[0008] Preferably, in step S1, the hot melt toughening adhesive layer is a hot melt adhesive modified by blending EVA and POE, wherein the mass percentage of POE is 15%-30%, and the melting temperature of the adhesive layer is 90-120℃.

[0009] Preferably, in step S2, the double-layer reverse folding specifically involves folding the edge of the bag body once towards the inside of the bag body, and then folding it once towards the outside of the bag body. The width of the two folds is the same, and after folding, a four-layer non-woven fabric overlapping edge sealing structure is formed.

[0010] Preferably, in step S2, the breaking elongation of the PP reinforcing fiber is 20%-35%, and the difference between the melting temperature of the fiber and the melting temperature of the nonwoven fabric substrate does not exceed 10°C.

[0011] Preferably, in step S3, the welding surface of the ultrasonic welding head is provided with a grid-like raised texture, the raised height is 0.05-0.15mm, and the grid spacing is 1-3mm.

[0012] Preferably, in step S3, during the three-level gradient welding process, the traveling speed of the hot press roller and the ultrasonic welding head is consistent with the conveying speed of the nonwoven bag, and the speed range is 5-15m / min.

[0013] Preferably, in step S4, during the three-stage gradient cooling process, the temperature difference between two adjacent cooling stages is controlled at 20-40℃ to avoid excessive temperature stress inside the sealing edge.

[0014] Preferably, in step S5, the contact angle of the sealing surface after secondary surface treatment is ≤65°, and the elongation at break at the sealing edge is increased by 10%-20% compared with that before treatment.

[0015] Preferably, the substrate of the nonwoven bag is PP spunbond nonwoven fabric with a basis weight of 30-120g / m2, the width of the final formed edge seal is 8-15mm, and the peel strength at the edge seal is ≥12N / 15mm.

[0016] (iii) Beneficial technical effects Compared with existing technologies, the beneficial effects of this invention are: Through edge pretreatment, the surface of the nonwoven fabric substrate was activated, modified, and its performance regulated. This effectively enhanced the bonding activity of the nonwoven fabric surface, improved the compatibility and adhesion between the adhesive layer and the substrate, and avoided problems such as incomplete welding and delamination during the welding process, laying a solid foundation for stable edge sealing. The edge preforming and reinforcement embedding processes optimized the overlapping structure of the edge sealing. Simultaneously, the reinforcement structure effectively dispersed the stress on the edge sealing during bending and load-bearing processes, preventing cracking caused by stress concentration and significantly improving the tear resistance and bending fatigue resistance of the edge sealing.

[0017] A gradient composite welding and sealing process is adopted, which achieves uniform and dense fusion of non-woven fibers, adhesive layers, and reinforcing structures through the coordinated operation of multiple welding steps. This avoids the problem of insufficient welding caused by single welding processes and eliminates substrate embrittlement defects caused by over-melting. While ensuring the welding strength of the edge sealing, the toughness of the substrate itself is preserved, significantly improving the batch stability of the edge sealing performance. Through a gradient cooling and shaping process, the problem of internal stress in the edge sealing caused by rapid cooling is avoided, ensuring the long-term stability of the edge sealing structure and eliminating warping and cracking problems caused by the release of internal stress later. Attached Figure Description

[0018] Figure 1 This is a flowchart of the edge sealing process for anti-cracking nonwoven bags disclosed in this invention; Figure 2 This is a graph comparing the peel strength and transverse breaking strength of the edge sealing in the examples and comparative examples using a bar graph. Figure 3 This is a line graph comparing the strength retention rate after high and low temperature cycling and the strength retention rate after UV accelerated aging of the examples and comparative examples; Figure 4 This is a radar comparison chart created by standardizing the dimensions of the performance comparison data of the examples and comparative examples. Detailed Implementation

[0019] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: The edge sealing process of the anti-cracking nonwoven bag of the present invention will be further described in detail below with reference to specific embodiments and comparative examples. In the following embodiments and comparative examples, unless otherwise specified, the melting temperature of the polypropylene (PP) spunbond nonwoven fabric substrate is 155-165℃, the hot melt toughening adhesive layer is a hot melt adhesive modified by blending ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer (POE), the melting temperature difference between the PP reinforcing fiber filament and the nonwoven fabric substrate does not exceed 10℃, and the conveying speed of the entire processing equipment can be synchronously controlled to meet the continuous production needs of nonwoven bags. Example

[0020] This embodiment is for conventional non-woven bags used in supermarket retail, using PP spunbond non-woven fabric substrate with a basis weight of 50g / ㎡, and the final edge sealing width is 8mm. The specific sealing process is carried out according to the following steps: S1 Edge preprocessing: First, the cut non-woven fabric bag blank is conveyed to a brush negative pressure dedusting unit to clean and remove impurities from the edge of the bag to be sealed. Two sets of forward and reverse brush rollers operating in the same direction brush off loose fibers and debris generated by edge cutting, and the brushed-off impurities are synchronously sucked away in real time through the supporting negative pressure air duct, so as to ensure the edge surface is clean and free of foreign matters and prevent impurities from affecting the subsequent welding bonding force. After cleaning, the bag edge is conveyed to a low-temperature plasma treatment device to perform surface activation treatment on the edge region with a width of 10 mm. The treatment adopts a mixed gas of argon and nitrogen as the working gas, in which the volume fraction of argon is 60% and the volume fraction of nitrogen is 40%, the treatment power is set to 80 W, and the treatment time is 10 s. Polar active groups are introduced on the surface of the non-woven fabric fibers through plasma bombardment, which greatly improves the wettability and bonding activity of the fiber surface. After the activation treatment, closed-loop humidity regulation is performed on the edge region through a constant-temperature constant-humidity regulation bellows for a regulation duration of 8 s, so that the moisture content of the non-woven fabric at the edge is stably controlled at 0.8% to prevent the fluctuation of moisture content from affecting the welding stability. Then, a hot-melt toughening adhesive layer is uniformly coated on the bonding surfaces of the upper and lower layers of the edge to be sealed by a micro-gravure coater, the coating thickness of the adhesive layer is precisely controlled to 0.02 mm, wherein the mass fraction of POE in the adhesive layer is 15%, and the melting temperature is 90 °C. After glue coating, the surface of the adhesive layer is gently blown with low-pressure cold air to avoid premature adhesion of the adhesive layer, and the whole process of edge preprocessing is completed.

[0021] S2 Edge-folding preforming and reinforcement embedding: The preprocessed bag edge is continuously conveyed to a numerical control edge folder to perform double-layer reverse folding on the edge. The specific operation process is as follows: first, the bag edge is horizontally folded once along the folding line toward the inner side of the bag, the folding width is precisely controlled to 8 mm, and then it is reversely folded once toward the outer side of the bag, the widths of the two folds are completely the same, and a basic edge-sealing structure formed by four layers of non-woven fabric laminated is formed after folding, which greatly improves the basic tear resistance of the sealed edge. During the folding process, a plurality of parallel arranged PP reinforcing fiber filaments are uniformly embedded in the inner bonding surface after the first fold through the high-precision fiber filament pay-off stand matched with the edge folder. The fiber filaments have a diameter of 0.1 mm, the spacing between adjacent fiber filaments is 5 mm, and the fiber filaments are continuously laid along the entire length of the sealed edge without breakpoints or offset. After the second reverse folding, the fiber filaments are completely wrapped between the two folded layers without exposure or dislocation. After the folding and filament embedding are completed, the folded edge is immediately subjected to cold pressure pre-shaping by a cold pre-shaping machine, the cold pressure is set to 0.2 MPa, and the pre-shaping time is 5 s, so that the folded layers and the internal fiber filaments are closely attached without warped edges or interlayer gaps, and a preformed sealed edge blank with a stable structure is obtained.

[0022] S3 Gradient Composite Welding and Sealing: The pre-formed edge-sealing blank is synchronously conveyed to the three-stage gradient composite welding unit. The travel speed of the entire line of equipment is consistent with the conveying speed of the non-woven bag, set at 5m / min. The three-stage continuous welding process is completed sequentially: First, a mirror-finish low-temperature hot press roller is used for low-temperature pre-melting. The temperature of the hot press roller is precisely controlled at 110℃, the hot pressing pressure is 0.3MPa, and the pre-melting time is 3s. This step allows the hot-melt toughening adhesive layer to completely melt, fully impregnate the non-woven fibers and PP reinforcing fibers, and simultaneously soften the surface fibers of the non-woven fabric, laying a uniform bonding foundation for subsequent deep welding. Then, it is conveyed to the ultrasonic welding station, where a 20kHz ultrasonic welding head is used for medium-frequency welding. The welding surface of the welding head has a mesh. The raised texture has a height of 0.05mm and a grid spacing of 3mm. The welding pressure is set at 0.4MPa and the welding time is 2s. Through ultrasonic high-frequency mechanical vibration, the molten adhesive layer and the softened non-woven fabric fibers and reinforcing fibers form an interpenetrating network structure, achieving a dense bond between the internal layers of the edge seal. At the same time, it avoids the problem of fiber over-melting and embrittlement caused by a single hot pressing process. Finally, it is conveyed to the mirror high-temperature hot press roller station for high-temperature shaping and fusion. The temperature of the hot press roller is precisely controlled at 135℃, the hot pressing pressure is 0.5MPa, and the fusion time is 4s. This ensures that the fusion structure of the edge seal is completely shaped, eliminates the micro-bubbles generated during the fusion process, and ensures that the bonding between the layers of the edge seal is uniform and without delamination, completing a complete edge sealing fusion.

[0023] S4 Gradient Cooling and Shaping: The edge sealing after welding is immediately and continuously conveyed to a three-stage gradient cooling and pressure holding unit. Throughout the cooling process, a constant pressure of 0.1 MPa is continuously applied to the edge sealing to prevent warping, shrinkage, and interlayer separation during cooling. The three-stage gradient cooling is completed sequentially: First, 40°C circulating warm air is used for pre-cooling for 6 seconds, allowing the edge sealing temperature to drop slowly and evenly, initially shaping the welded joint structure; then, 15°C clean cold air is used for medium-speed cooling for 10 seconds, further stabilizing the edge sealing temperature; finally, 5°C low-temperature mirror cooling rollers are used for roll cooling for 4 seconds, rapidly reducing the edge sealing temperature to room temperature, completing the overall cooling and shaping. In this step, the temperature difference between adjacent cooling stages is stably controlled at 25°C to avoid excessive temperature stress inside the edge sealing due to sudden temperature changes, thereby reducing the risk of later cracking caused by internal stress release.

[0024] S5 Edge Sealing Toughening Treatment: The cooled and shaped edge seal is transported to a secondary low-temperature plasma treatment device. A secondary surface toughening treatment is performed on both sides of the edge seal using a processing power of 60W for 6 seconds. This further optimizes the fiber structure of the edge seal surface, repairs micro-damage to the surface fibers that may occur during the welding process, and improves the toughness and anti-aging performance of the edge seal. After treatment, the contact angle of the edge seal surface is ≤65°, and the elongation at break at the edge seal is increased by more than 10% compared with that before treatment. Finally, the sealing process of the non-woven bag edge is completed, and the peel strength of the finished edge seal is ≥12N / 15mm. Example

[0025] This embodiment is for high-load-bearing daily-use non-woven bags, using PP spunbond non-woven fabric substrate with a basis weight of 80g / ㎡, and the final edge sealing width is 12mm. The specific sealing process is carried out according to the following steps: S1 Edge Pretreatment: First, the cut non-woven bag blanks are conveyed to the brush negative pressure dust collector unit to clean and remove impurities from the edges of the bags to be sealed. Two sets of brush rollers rotating in the same direction remove loose lint and debris generated during edge cutting. Simultaneously, the brushed impurities are sucked away in real time through the corresponding negative pressure air duct to ensure the edge surface is clean and free of foreign objects. After cleaning, the bag edges are conveyed to a low-temperature plasma treatment device for surface activation treatment of the 15mm wide edge area. The treatment uses a mixture of argon and nitrogen as the working gas, with argon accounting for 70% of the volume and nitrogen accounting for 30%. The treatment power is set to 120W, and the treatment time is 6s. The process involves introducing polar active groups onto the surface of nonwoven fabric fibers through plasma bombardment, thereby enhancing the wettability and bonding activity of the fiber surface. After activation treatment, a closed-loop humidity control system is used in the edge area via a constant temperature and humidity control box for 10 seconds to stabilize the moisture content of the edge nonwoven fabric at 1.5%. Subsequently, a hot-melt toughening adhesive layer is uniformly coated onto the upper and lower bonding surfaces of the edge to be sealed using a micro-gravure adhesive coating machine. The coating thickness is precisely controlled to 0.05 mm, with POE accounting for 22% of the adhesive layer by mass and a melting temperature of 105°C. After coating, the adhesive layer surface is gently blown with low-pressure cold air to prevent premature adhesion, thus completing the edge pretreatment process.

[0026] S2 Edge-folding preforming and reinforcement embedding: The preprocessed bag edge is continuously conveyed to a numerically controlled edge-folding machine to perform double-layer reverse folding on the edge. The specific operation process is as follows: first, the bag edge is horizontally folded once along the folding line toward the inner side of the bag body, with the folding width precisely controlled at 12mm, and then reversely folded once toward the outer side of the bag body, the widths of the two folds are completely consistent, and a sealing edge base structure formed by four layers of non-woven fabrics laminated is obtained after folding; during the folding process, a plurality of parallel-arranged PP reinforcing fiber filaments are uniformly embedded on the inner bonding surface after the first folding through the high-precision filament pay-off stand matched with the edge-folding machine, the diameter of the fiber filaments is 0.2mm, the spacing between adjacent fiber filaments is 3.5mm, the fiber filaments are continuously laid along the entire length of the sealing edge without breakpoints or offsets, and after the second reverse folding, the fiber filaments are completely wrapped between the two folding layers without exposure or misalignment; after the folding and filament embedding is completed, the folded edge is immediately subjected to cold pre-shaping through a cold pre-shaping machine, the cold pressing pressure is set to 0.3MPa, and the pre-shaping time is 3.5s, so that the folded layers are closely attached to the internal fiber filaments without edge warping or interlayer gaps, and a preformed sealing edge blank with a stable structure is obtained.

[0027] S3 Gradient composite fusion sealing: The preformed sealing edge blank is synchronously conveyed to a three-stage gradient composite fusion unit, the traveling speed of the whole line of equipment is consistent with the conveying speed of the non-woven bag, which is set to 10m / min, and three stages of continuous fusion treatment are completed in sequence: firstly, a mirror low-temperature hot pressing roller is used for low-temperature pre-fusion, the temperature of the hot pressing roller is precisely controlled at 120°C, the hot pressing pressure is 0.4MPa, and the pre-fusion time is 2s. In this step, the hot-melt toughening adhesive layer is completely melted to fully infiltrate the non-woven fabric fibers and the PP reinforcing fiber filaments, and at the same time, the surface fibers of the non-woven fabric are softened synchronously; then the workpiece is conveyed to the ultrasonic welding station, and a 28kHz ultrasonic welding head is used for intermediate-frequency fusion. The welding surface of the welding head is provided with grid-shaped raised textures with a raised height of 0.1mm and a grid spacing of 2mm, the welding pressure is set to 0.5MPa, and the fusion time is 1.2s. Through the high-frequency mechanical vibration of ultrasonic waves, the molten adhesive layer forms an interpenetrating network structure with the softened non-woven fabric fibers and reinforcing fiber filaments, so as to realize the dense combination of all layers inside the sealing edge; finally, the workpiece is conveyed to the mirror high-temperature hot pressing roller station for high-temperature shaping and fusion. The temperature of the hot pressing roller is precisely controlled at 142°C, the hot pressing pressure is 0.6MPa, and the fusion time is 3s, so that the fusion structure of the sealing edge is completely shaped, tiny bubbles generated during the fusion process are eliminated, the combination between all layers of the sealing edge is uniform without delamination, and the complete edge sealing fusion is completed.

[0028] S4 Gradient Cooling and Shaping: The edge sealing after welding is immediately and continuously conveyed to a three-stage gradient cooling and pressure holding unit. Throughout the cooling process, a constant pressure of 0.15MPa is continuously applied to the edge sealing to prevent warping, shrinkage, and interlayer separation during cooling. The three-stage gradient cooling is completed sequentially: First, 50℃ circulating warm air is used for pre-cooling for 4.5s, allowing the edge sealing temperature to drop slowly and evenly, initially shaping the welded joint structure; then, 20℃ clean cold air is used for medium-speed cooling for 7.5s, further stabilizing the edge sealing temperature; finally, 8℃ low-temperature mirror cooling rollers are used for roll cooling for 3s, rapidly reducing the edge sealing temperature to room temperature, completing the overall cooling and shaping. In this step, the temperature difference between adjacent cooling stages is stably controlled at 30℃ to avoid excessive temperature stress inside the edge sealing due to sudden temperature changes, thereby reducing the risk of later cracking caused by internal stress release.

[0029] S5 Edge Sealing Toughening Treatment: The cooled and shaped edge seal is transported to a secondary low-temperature plasma treatment device. A secondary surface toughening treatment is performed on both sides of the edge seal using a processing power of 80W for 4 seconds. This further optimizes the fiber structure of the edge seal surface, repairs micro-damage to the surface fibers that may occur during the welding process, and improves the toughness and anti-aging performance of the edge seal. After treatment, the contact angle of the edge seal surface is ≤65°, and the elongation at break at the edge seal is increased by more than 15% compared with that before treatment. Finally, the sealing process of the non-woven bag edge is completed, and the peel strength of the finished edge seal is ≥15N / 15mm. Example

[0030] This embodiment is for heavy-duty non-woven bags used in warehousing and logistics. It uses PP spunbond non-woven fabric substrate with a basis weight of 120g / ㎡, and the final edge sealing width is 15mm. The specific sealing process is performed according to the following steps: S1 Edge preprocessing: First, the cut non-woven fabric bag preform is conveyed to a brush negative pressure dust removal unit to clean and remove impurities from the edge of the bag to be sealed. Two sets of forward and reverse brush rollers rotating in the same direction brush off loose fibers and debris generated by edge cutting, and the brushed-off impurities are sucked away in real time through the supporting negative pressure air duct, so as to ensure that the edge surface is clean and free of foreign matters; after cleaning, the bag edge is conveyed to a low-temperature plasma treatment device to perform surface activation treatment on the edge area with a width of 20mm. The treatment uses a mixed gas of argon and nitrogen as the working gas, in which the volume fraction of argon is 80% and the volume fraction of nitrogen is 20%. The treatment power is set to 150W, and the treatment time is 3s. Polar active groups are introduced on the surface of the non-woven fabric fibers through plasma bombardment, so as to improve the wettability and bonding activity of the fiber surface; after the activation treatment, closed-loop humidity regulation is performed on the edge area through a constant temperature and humidity regulation bellows for a regulation duration of 12s, so that the moisture content of the non-woven fabric at the edge is stably controlled at 2.5%; then, a hot-melt toughening adhesive layer is evenly coated on the bonding surfaces of the upper and lower layers of the edge to be sealed by a micro-gravure coater, and the coating thickness of the adhesive layer is precisely controlled to 0.08mm, wherein the mass fraction of POE in the adhesive layer is 30%, and the melting temperature is 120°C. After glue coating, the surface of the adhesive layer is gently blown by low-pressure cold air to avoid premature adhesion of the adhesive layer, and the whole process of edge preprocessing is completed.

[0031] S2 Edge-folding preforming and reinforcement embedding: The preprocessed bag edge is continuously conveyed to a numerical control edge folder to perform double-layer reverse folding on the edge. The specific operation process is as follows: first, the bag edge is horizontally folded once along the folding line toward the inner side of the bag, the folding width is precisely controlled to 15mm, then it is reversely folded once toward the outer side of the bag, the widths of the two folds are completely consistent, and a basic edge-sealing structure formed by laminating four layers of non-woven fabrics is obtained after folding; during the folding process, through the high-precision fiber pay-off rack matched with the edge folder, a plurality of parallel-arranged PP reinforcing fiber filaments are evenly embedded on the inner bonding surface after the first folding, the diameter of the fiber filaments is 0.3mm, the spacing between adjacent fiber filaments is 2mm, the fiber filaments are continuously laid along the entire length of the edge seal without breakpoints or offsets. After the second reverse folding, the fiber filaments are completely wrapped between the two folded layers without exposure or misalignment; after the folding and filament embedding are completed, the folded edge is immediately subjected to cold pressure pre-shaping by a cold pre-shaping machine, the cold pressure is set to 0.4MPa, and the pre-shaping time is 2s, so that the folded layers and the internal fiber filaments are closely attached without edge warping or interlayer gaps, and a preformed edge-sealing preform with a stable structure is obtained.

[0032] S3 Gradient Composite Welding and Sealing: The pre-formed edge-sealing blank is synchronously conveyed to the three-stage gradient composite welding unit. The travel speed of the entire line of equipment is consistent with the conveying speed of the non-woven bag, set at 15m / min. Three-stage continuous welding processes are completed sequentially: First, a mirror-finished low-temperature hot press roller is used for low-temperature pre-melting. The temperature of the hot press roller is precisely controlled at 130℃, the hot pressing pressure is 0.5MPa, and the pre-melting time is 1s. This step ensures that the hot-melt toughening adhesive layer is completely melted, fully impregnating the non-woven fibers and PP reinforcing fibers, while simultaneously softening the surface fibers of the non-woven fabric. Then, it is conveyed to the ultrasonic welding station, where a 35kHz ultrasonic welding head is used for medium-frequency welding. The welding surface of the welding head is equipped with… The mesh-like raised texture has a raised height of 0.15mm and a mesh spacing of 1mm. The welding pressure is set at 0.6MPa and the welding time is 0.5s. Through ultrasonic high-frequency mechanical vibration, the molten adhesive layer and the softened non-woven fabric fibers and reinforcing fibers form an interpenetrating network structure, achieving a dense bond between the internal layers of the edge seal. Finally, it is conveyed to the mirror-finish high-temperature hot press roller station for high-temperature shaping and fusion. The temperature of the hot press roller is precisely controlled at 150℃, the hot press pressure is 0.7MPa, and the fusion time is 2s, so that the fusion structure of the edge seal is completely shaped, eliminating the micro-bubbles generated during the fusion process, ensuring that the bonding between the layers of the edge seal is uniform and without delamination, and completing the complete edge sealing fusion.

[0033] S4 Gradient Cooling and Shaping: The edge sealing after welding is immediately and continuously conveyed to a three-stage gradient cooling and pressure holding unit. Throughout the cooling process, a constant pressure of 0.2MPa is continuously applied to the edge sealing to prevent warping, shrinkage, and interlayer separation during cooling. The three-stage gradient cooling is completed sequentially: First, 60℃ circulating warm air is used for pre-cooling for 3 seconds, allowing the edge sealing temperature to drop slowly and evenly, initially shaping the welded joint structure; then, 25℃ clean cold air is used for medium-speed cooling for 5 seconds, further steadily reducing the edge sealing temperature; finally, 10℃ low-temperature mirror cooling rollers are used for roll cooling for 2 seconds, rapidly reducing the edge sealing temperature to room temperature, completing the overall cooling and shaping. In this step, the temperature difference between adjacent cooling stages is stably controlled at 35℃ to avoid excessive temperature stress inside the edge sealing due to sudden temperature changes, thereby reducing the risk of later cracking caused by internal stress release.

[0034] S5 Edge Sealing Toughening Treatment: The cooled and shaped edge seal is transported to a secondary low-temperature plasma treatment device. A secondary surface toughening treatment is performed on both sides of the edge seal using a processing power of 100W for 2 seconds. This further optimizes the fiber structure of the edge seal surface, repairs micro-damage to the surface fibers that may occur during the welding process, and improves the toughness and anti-aging performance of the edge seal. After treatment, the contact angle of the edge seal surface is ≤65°, and the elongation at break at the edge seal is increased by more than 20% compared with that before treatment. Finally, the sealing process of the non-woven bag edge is completed, and the peel strength of the finished edge seal is ≥18N / 15mm.

[0035] Comparative Example 1 This comparative example employs a conventional single hot-press welding process, using the same 50g / m² PP spunbond nonwoven fabric substrate as Example 1, with a target edge sealing width of 8mm. The specific process involves: after simple manual cleaning of the edges of the nonwoven bag blank, a single-layer fold is performed with a fold width of 8mm. Then, a single set of hot-press rollers at 150℃ is used for one-time hot-press welding. The hot-press pressure is set to 0.5MPa, and the welding time is 5s. After welding, the bag is immediately cooled with room temperature cold air for 5s to complete the edge sealing. This comparative example does not utilize all the core processes of this invention, including low-temperature plasma activation pretreatment, toughening adhesive coating, double-layer reverse folding structure, PP reinforcing fiber embedding, three-stage gradient composite welding, gradient cooling and pressure holding, and secondary plasma toughening treatment.

[0036] Comparative Example 2 This comparative example employs a conventional single ultrasonic welding process found in existing technologies. It uses the same 80g / m² PP spunbond nonwoven fabric substrate as Example 2, with a target edge sealing width of 12mm. The specific process involves: after simple manual cleaning of the edges of the nonwoven bag blank, it is folded into a single layer with a fold width of 12mm. Then, a 28kHz ultrasonic welding head is used for a one-time welding operation. The welding pressure is set to 0.5MPa, and the welding time is 2 seconds to complete the edge sealing. This comparative example does not employ all the core processes of this invention, including low-temperature plasma activation pretreatment, toughening adhesive coating, double-layer reverse folding structure, PP reinforcing fiber embedding, three-level gradient composite welding, gradient cooling and pressure holding, and secondary plasma toughening treatment.

[0037] Comparative Example 3 This comparative example omits several core processes of the present invention. It uses the same 80g / m² PP spunbond nonwoven fabric substrate as Example 2, with a target edge sealing width of 12mm. The specific process is as follows: after simple cleaning and impurity removal of the bag edges, a hot melt adhesive layer of the same specification as in Example 2 is applied, followed by single-layer folding. PP reinforcing fibers are not embedded. A single set of hot-press rollers at 140℃ is used for one-time hot-press welding. After welding, room temperature cold air is used for rapid cooling, without gradient cooling pressure holding or secondary plasma toughening treatment. This comparative example omits the core processes of plasma activation modification, double-layer reverse folding structure, reinforcing fiber embedding, three-stage gradient welding, gradient cooling pressure holding, and secondary toughening treatment.

[0038] Performance testing verified that the nonwoven bag edge seals prepared in Examples 1-3 showed no cracking, delamination, or degumming after 1000 repeated bending cycles. Their edge seal peel strength, tear resistance, and bending fatigue resistance were significantly superior to those of Comparative Examples 1-3, making them suitable for the production needs of nonwoven bags with different load-bearing capacities. In contrast, the edge seals prepared in Comparative Examples 1-3 all exhibited obvious cracking and delamination after 100-300 repeated bending cycles, demonstrating low edge seal peel strength and a tendency to fail under load. This fully demonstrates the technical advantages and crack-prevention effect of the process described in this invention.

[0039] The core mechanical properties of the nonwoven bag edge sealing in the examples and comparative examples are compared in the table below: Table 1

[0040] The following table compares the long-term stability and process adaptability of the nonwoven bags used in the examples and comparative examples for edge sealing: Table 2

[0041] In summary, the data in the two tables fully demonstrate that the edge sealing process of the anti-cracking nonwoven bag described in this invention is significantly superior to existing conventional and simplified sealing processes in terms of core mechanical properties, long-term stability, and process adaptability. It not only possesses higher peel strength, breaking strength, and bending fatigue life, but also exhibits tight interlayer bonding and extremely low embrittlement rate. Furthermore, it demonstrates high strength retention after high and low temperature cycling and UV aging, high mass production qualification rate, fast production speed adaptation, and low edge warping rate. It effectively solves the pain points of existing nonwoven bag edge sealing, such as easy cracking, unstable performance, and poor process adaptability, fully reflecting the technological advancement and practical value of the process described in this invention.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A crack-resistant nonwoven bag edge sealing process, characterized in that, Includes the following steps: S1 Edge Pretreatment: The edges of the nonwoven bag blank to be sealed are cleaned and impurities are removed. After removing edge lint and stains, the edge area with a width of 10-20mm is surface activated by low-temperature plasma with a treatment power of 80-150W and a treatment time of 3-10s. After treatment, the humidity of the edge area is controlled to keep the moisture content of the edge nonwoven fabric stable at 0.8%-2.5%. At the same time, a hot melt toughening adhesive layer with a thickness of 0.02-0.08mm is uniformly coated on the bonding surface of the edge to be sealed to complete the edge pretreatment. S2 edge preforming and reinforcement embedding: The pre-treated bag edge is double-folded in reverse, with a fold width of 8-15mm. After folding, multiple parallel PP reinforcement fibers are evenly embedded between the two folded layers. The fiber diameter is 0.1-0.3mm and the spacing between adjacent fibers is 2-5mm. After embedding, the folded edge is cold-pressed and pre-shaped with a pressure of 0.2-0.4MPa for 2-5s to obtain the pre-formed edge sealing blank. S3 Gradient Composite Welding and Sealing: The pre-formed edge sealing blank undergoes a three-stage gradient welding process. First, a low-temperature pre-melting is performed using a hot press roller at 110-130℃, with a hot pressing pressure of 0.3-0.5MPa and a pre-melting time of 1-3s. Then, a medium-frequency welding is performed using an ultrasonic welding head at 20-35kHz, with a welding pressure of 0.4-0.6MPa and a welding time of 0.5-2s. Finally, a high-temperature shaping and fusion is performed using a hot press roller at 135-150℃, with a hot pressing pressure of 0.5-0.7MPa and a fusion time of 2-4s, completing the edge sealing welding. S4 Gradient Cooling and Shaping: The welded edge seal is subjected to three-stage gradient cooling. First, it is pre-cooled with warm air at 40-60℃ for 3-6 seconds, then cooled with cold air at 15-25℃ for 5-10 seconds, and finally cooled with low-temperature roller pressing at 5-10℃ for 2-4 seconds. Throughout the cooling process, a holding pressure of 0.1-0.2MPa is continuously applied to the edge seal. S5 edge sealing toughening treatment: After cooling and shaping, the edge sealing is subjected to a secondary surface toughening treatment with 60-100W low-temperature plasma for 2-6 seconds, finally completing the sealing process of the non-woven bag edge.

2. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S1, the low-temperature plasma treatment uses a mixture of argon and nitrogen as the working gas, with argon accounting for 60%-80% of the volume and nitrogen accounting for 20%-40% of the volume.

3. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S1, the hot melt toughening adhesive layer is a hot melt adhesive modified by blending EVA and POE, wherein the mass percentage of POE is 15%-30%, and the melting temperature of the adhesive layer is 90-120℃.

4. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S2, the double-layer reverse folding specifically involves folding the edge of the bag body once towards the inside of the bag body, and then folding it once towards the outside of the bag body. The width of the two folds is the same, and after folding, a four-layer non-woven fabric overlapping edge sealing structure is formed.

5. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S2, the breaking elongation of the PP reinforcing fiber is 20%-35%, and the difference between the melting temperature of the fiber and the melting temperature of the nonwoven fabric substrate does not exceed 10℃.

6. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S3, the welding surface of the ultrasonic welding head is provided with a grid-like raised texture, the raised height is 0.05-0.15mm, and the grid spacing is 1-3mm.

7. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S3, during the three-level gradient welding process, the traveling speed of the hot press roller and the ultrasonic welding head is consistent with the conveying speed of the nonwoven bag, with a speed range of 5-15m / min.

8. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S4, during the three-stage gradient cooling process, the temperature difference between two adjacent cooling stages is controlled at 20-40℃ to avoid excessive temperature stress inside the sealing edge.

9. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, In step S5, the contact angle of the sealing surface after secondary surface treatment is ≤65°, and the elongation at break at the sealing edge is increased by 10%-20% compared with that before treatment.

10. The edge sealing process for anti-cracking nonwoven bags according to claim 1, characterized in that, The base material of the nonwoven bag is PP spunbond nonwoven fabric with a basis weight of 30-120 g / m². 2 The final edge sealing width is 8-15mm, and the peel strength at the edge sealing is ≥12N / 15mm.

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