Preparation process of moisture-proof and mildew-proof coating for non-woven fabric bag

Abstract

The application relates to the technical field of environment-friendly textile materials, and discloses a preparation process of a moisture-proof and mildew-proof coating of a non-woven fabric bag, which comprises the following steps: immersing a base material into a compounded alkaline degreasing solution for constant-temperature soaking, rinsing, and hot air drying until the water content is lower than 3%; mixing water-based polyurethane, a waterproof agent, a mildew-proof agent, a leveling agent, a crosslinking agent and deionized water according to a proportion, stirring at a low speed, high-speed dispersing, filtering, and obtaining a coating liquid; uniformly pulling the base material after immersion coating, pre-drying at a low temperature, and crosslinking and film forming through segmented heat curing, and obtaining a moisture-proof and mildew-proof non-woven fabric bag finished product after cooling and detection. The coating of the non-woven fabric bag is firmly combined with the base material, has strong compactness, can long-effectively prevent moisture and mildew, is environment-friendly and free of harmful solvents, retains the air permeability of the bag, is stable in process and easy to mass produce, can improve the durability of the non-woven fabric bag, and widens the use scenarios.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly textile materials technology, and in particular relates to the preparation process of moisture-proof and mildew-proof coating for non-woven bags. Background Technology

[0002] Non-woven bags, as green and environmentally friendly packaging and storage materials, are widely used in supermarkets, logistics and transportation, home storage, and product packaging due to their advantages such as being biodegradable, recyclable, and having low processing costs. They are a core environmentally friendly product that can replace disposable plastic packaging.

[0003] Non-woven bags are mostly made of polypropylene or polyester fibers through hot rolling and needle punching processes. The fibers have a natural porous structure, which provides basic breathability, but also makes them very easy to absorb moisture from the air. In humid and enclosed storage or use environments, moisture accumulation can easily cause the fibers to soften and lose strength, while also promoting the growth of mold, leading to mildew and damage to the bags. This not only affects the appearance and safety of use, but also significantly shortens their service life.

[0004] Traditional protective treatments for non-woven bags often involve lamination, waxing, or simple application of waterproof coatings. These processes have several limitations. Lamination materials have poor adhesion to the substrate, making them prone to peeling and detachment, compromising the bag's breathability. Waxed layers have poor heat resistance, softening and flowing at high temperatures and becoming brittle at low temperatures, resulting in extremely short-lived protection. Ordinary waterproof coatings often contain organic solvents, making them environmentally unfriendly, and their poor density prevents long-term protection against moisture and mold.

[0005] While existing water-based environmentally friendly coating processes have improved environmental performance, they still have shortcomings in core technologies. The coating adhesion to the non-woven fabric substrate is weak, leading to peeling and detachment during use; the moisture-proof components cannot form a continuous and dense barrier structure, allowing moisture to easily penetrate; the anti-mildew components are mostly added in a free manner, easily precipitating and failing, making long-term protection difficult; the coating preparation process is rough, with frequent problems such as insufficient curing and uneven thickness, resulting in poor product performance stability. As the application scenarios of non-woven bags continue to expand, the market's requirements for their comprehensive performance in terms of moisture-proofing, mildew-proofing, environmental protection, and durability are constantly increasing. Developing stable, highly effective, and environmentally friendly moisture-proof and mildew-proof coating preparation technologies has become an urgent problem for the industry. Summary of the Invention

[0006] To address the shortcomings of existing nonwoven bags, such as easy moisture absorption and mildew growth due to fiber pores, poor adhesion and easy peeling of traditional protective processes, insufficient density of water-based coatings, easy precipitation and failure of anti-mildew components, and unstable production processes, this invention provides a process for preparing a moisture-proof and mildew-proof coating for nonwoven bags.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The preparation process of the moisture-proof and mildew-proof coating for non-woven bags includes the following steps:

[0009] S1. A high-pressure clean air blowing device is used to perform all-round surface purification treatment on the non-woven bag substrate. The blowing air pressure is controlled at 0.3MPa-0.6MPa, the blowing air velocity is 15m / s-25m / s, and the blowing is continued for 5min-10min to remove floating dust, loose fibers and mechanical impurities attached to the substrate surface, thus completing the pre-treatment of substrate purification.

[0010] S2. Immerse the pretreated nonwoven bag substrate in an alkaline degreasing solution composed of sodium hydroxide, sodium carbonate and nonionic surfactant. Control the solution temperature at 35℃-50℃ and soak for 10min-25min. After soaking, rinse with deionized water in three stages of countercurrent rinsing until the pH value of the rinsing water is stable at 6.8-7.2.

[0011] S3. The rinsed non-woven bag substrate is sent into a hot air circulating drying oven, and the drying temperature is controlled at 65℃-85℃, the circulating air speed is 3m / s-8m / s, and the drying is continued for 15min-35min, so that the final moisture content of the substrate is controlled below 3%, and a clean and dry coating non-woven bag substrate is obtained.

[0012] S4. Weigh out the following ingredients according to the preset mass proportions: waterborne polyurethane emulsion with a solid content of 30%-40%, hydroxyl silicone oil waterproofing agent, chitosan quaternary ammonium salt mildew inhibitor, polyether modified organosilicon leveling agent, aziridine crosslinking agent, and deionized water. Add the above raw materials to the stirred reactor in sequence and stir at a low speed of 300r / min-500r / min for 15min-20min to obtain the coating mixture base material.

[0013] S5. Transfer the coating mixture into a high-speed shear disperser, control the dispersion speed at 1000r / min-2800r / min and the dispersion temperature at 20℃-30℃, disperse at high speed for 10min-20min, so that the particle size of the mixture is less than 10μm, and obtain a uniform and stable moisture-proof and mildew-proof coating liquid.

[0014] S6. Vertically immerse the dried non-woven bag substrate into the moisture-proof and mildew-proof coating liquid, controlling the immersion time to be 3min-7min, so that the substrate fibers can fully absorb the coating liquid. Then, vertically lift it at a uniform speed of 0.6m / min-1.8m / min, controlling the wet film thickness of the coating to be 35μm-75μm, to ensure that the coating is evenly adhered to the substrate surface without any missed coating or drips.

[0015] S7. First, put the non-woven bag substrate that has been dip-coated into a low-temperature pre-drying oven, control the temperature at 45℃-65℃, pre-dry for 5min-12min to remove free moisture on the coating surface, and then transfer it into a hot air curing oven, control the temperature at 115℃-145℃, heat cure for 10min-20min to allow the coating to complete the cross-linking film formation reaction.

[0016] S8. Remove the heat-cured nonwoven bag from the curing oven and allow it to cool naturally at room temperature for 20-30 minutes until the product temperature drops below 25°C. After passing the appearance and coating adhesion tests, the finished moisture-proof and mildew-proof nonwoven bag is obtained.

[0017] Preferably, after the moisture-proof and mildew-proof coating liquid is prepared, the pH value of the coating liquid is finely adjusted to control the pH value of the system at 5.5-7.0, which triggers the hydrolysis and condensation reaction of the hydroxyl silicone oil waterproofing agent. The reaction molecular formula is (CH3)2Si(OC2H5)2+2H2O→(CH3)2Si(OH)2+2C2H5OH, 2(CH3)2Si(OH)2→(CH3)2SiOSi(CH3)2+H2O. The generated siloxane cross-linked structure can improve the hydrophobic and moisture-proof performance of the coating.

[0018] Preferably, during the thermosetting process, a cross-linking film-forming reaction is triggered by a high-temperature environment between the aziridine cross-linking agent and the hydroxyl and carboxyl groups on the waterborne polyurethane molecular chain. The reaction molecular formula is PU-OH+RN(CH2CH2)→PU-O-CH2CH2-NH-R, forming a three-dimensional network polymer structure, which enhances the density, adhesion and abrasion resistance of the coating.

[0019] Preferably, the mass fraction of each component in the alkaline degreasing solution in S2 is 3%-5% sodium hydroxide, 2%-5% sodium carbonate, and 0.5%-1% nonionic surfactant, with a total mass fraction of 5%-12%. During the soaking process, a low-speed stirring device is used to drive the solution flow and improve the degreasing effect. The stirring speed is 100r / min-200r / min.

[0020] Preferably, the relative humidity of the hot air circulating drying oven in S3 is controlled at 20%-30%. During the drying process, the moisture content of the substrate is checked every 5 minutes, and the drying temperature and wind speed are adjusted in real time to keep the moisture content of the substrate stable below 3% and avoid residual moisture from affecting the adhesion and curing effect of the coating.

[0021] Preferably, the process further includes, during the preparation of the coating mixture base material, allowing the chitosan quaternary ammonium salt antifungal agent to undergo a coordination antibacterial reaction with zinc ions in the system, the reaction having the molecular formula (C6H) 11 NO4) n +nZn 2+ →[C6H9NO4Zn]n +2nH + The generated coordination compounds can disrupt the cell membrane structure of microorganisms, achieving long-lasting and broad-spectrum antifungal and antibacterial effects, and extending the storage life of non-woven bags.

[0022] Preferably, the dip coating process in S6 is carried out in a clean and sealed dip coating tank with a cleanliness level of 10,000. The temperature of the coating liquid is kept constant at 25°C. During the lifting process, the substrate is kept vertical and without tilting to ensure that the coating thickness uniformity deviation is controlled within 5μm.

[0023] Preferably, the low-temperature pre-baking and heat curing process in S7 adopts a segmented temperature control mode. In the pre-baking stage, the temperature is uniformly increased to the target temperature at a rate of 5℃ / min, and in the heat curing stage, the temperature is uniformly increased at a rate of 8℃ / min. This avoids sudden temperature changes that may cause cracking, blistering, or peeling defects in the coating, thus ensuring the coating forming quality.

[0024] Preferably, after the high-speed shear dispersion treatment in S5, a microporous filtration device with a precision of 10μm is used to pressurize and filter the moisture-proof and mildew-proof coating liquid at a filtration pressure of 0.2MPa-0.3MPa to remove large particulate impurities and undispersed agglomerates in the system, thereby improving the fineness of the coating liquid and the smoothness of the film formation.

[0025] Preferably, after thermosetting, the silicone molecules inside the coating undergo a copolymerization reaction with the waterborne polyurethane molecules, with the reaction formula being -Si-OH+HO-PU→-Si-O-PU-+H2O, forming an interpenetrating polymer network structure. This further enhances the mechanical properties, moisture-proof sealing, and mildew-proof durability of the coating, broadening the applicable environment range of the nonwoven bag.

[0026] The present invention has the following beneficial effects:

[0027] This invention uses a refined substrate pretreatment process to remove impurities and grease from the surface of nonwoven bags, enhance the bonding strength between the coating and the fiber substrate, and ensure long-term stable adhesion between the coating and the substrate.

[0028] It adopts an environmentally friendly water-based polymer compound system, combined with green waterproof and mildew-proof components, with no harmful solvents added throughout the process. The coating has excellent biocompatibility and environmental friendliness, which is in line with the environmentally friendly application attributes of non-woven bags.

[0029] The coating undergoes multiple cross-linking reactions to form a three-dimensional interpenetrating network structure, which greatly improves its density and effectively blocks the intrusion of external moisture. This fundamentally prevents the non-woven bag from absorbing moisture and becoming brittle, achieving long-lasting and efficient moisture protection.

[0030] The anti-mold components are stably immobilized in the coating through coordination reactions, making them less prone to precipitation and loss. They can continuously inhibit the growth and metabolism of mold, achieving long-lasting and broad-spectrum anti-mold properties and effectively extending the storage and service life of non-woven bags.

[0031] The segmented temperature-controlled curing process ensures uniform and complete coating formation, avoiding defects such as cracking, blistering, and sagging, while improving the mechanical strength and abrasion resistance of the coating, making it suitable for various application scenarios.

[0032] The coating ensures moisture and mildew resistance while maintaining the basic breathability of the non-woven bag, avoiding stuffiness in a closed environment, thus balancing protection and user experience.

[0033] The coating preparation process parameters are standardized and highly controllable, which can ensure that the performance of different batches of products is stable and consistent, making it suitable for industrial mass production and effectively improving product yield and production efficiency.

[0034] The molded coating has excellent weather resistance and can be used in different temperature and humidity environments. Its performance is not easily degraded by the environment, which comprehensively improves the overall performance of non-woven bags and broadens their application range. Attached Figure Description

[0035] Figure 1 This invention provides a process flow diagram for preparing the moisture-proof and mildew-proof coating on non-woven bags;

[0036] Figure 2 This is a comparison chart of the adhesion scores of different sample coatings proposed in this invention;

[0037] Figure 3 This is a graph showing the relationship between the substrate moisture content and moisture-proof efficiency proposed in this invention.

[0038] Figure 4 This is a comparison chart of the overall performance of Embodiment 2 and Comparative Example 1 proposed in this invention;

[0039] Figure 5 This is a graph showing the relationship between thermosetting temperature and coating density proposed in this invention. Detailed Implementation

[0040] This specific implementation method is carried out entirely in a Class 10,000 cleanroom environment for environmentally friendly material processing. The ambient temperature is controlled between 20℃ and 30℃, and the relative humidity is controlled between 40% and 60%. All processing equipment has undergone clean treatment, and the raw materials are all environmentally friendly industrial-grade components, free of heavy metals and harmful volatile substances. The core innovation of this invention lies in the entire process of preparing a dense and stable moisture-proof and mildew-proof coating through refined substrate pretreatment, environmentally friendly coating compounding, multi-dimensional cross-linking curing, and segmented temperature-controlled molding, thus solving the technical problems of traditional non-woven bags being prone to moisture absorption, mildew, and coating peeling. This implementation method includes three sets of preferred embodiments and one set of traditional process comparative examples. All process steps are fully elaborated, parameters are comprehensively detailed, and process parameters and molding effects can be verified by conventional testing equipment.

[0041] Core chemical reaction formula:

[0042] Hydroxysilicone oil hydrolysis-condensation reaction:

[0043] (CH3)2Si(OC2H5)2+2H2O (CH3)2Si(OH)2+2C2H5OH

[0044] 2(CH3)2Si(OH)2 (CH3)2SiOSi(CH3)2+H2O

[0045] The crosslinking reaction between aziridine crosslinking agent and polyurethane:

[0046] PU-OH+RN(CH2CH2) PU-O-CH2CH2-NH-R

[0047] Coordination reaction of chitosan quaternary ammonium salt with zinc ions:

[0048] (C6H 10 O4N∙N(CH3)3) n +nZn 2+ →[(C6H 10 O4N∙N(CH3)3)2Zn] n +2nH +

[0049] Copolymerization and bonding reaction of organosilicon and polyurethane:

[0050] -Si-OH+HO-PU -Si-O-PU-+H2O.

[0051] Example 1

[0052] S1. A high-pressure clean air blowing device is used to perform all-round surface purification treatment on the polypropylene non-woven bag substrate. The blowing air pressure is controlled at 0.3MPa and the blowing air velocity is 15m / s. The blowing is continued for 5 minutes to remove floating dust, loose fibers and mechanical impurities from the substrate surface, thus completing the substrate purification pretreatment.

[0053] S2. Immerse the pretreated nonwoven bag substrate in an alkaline degreasing solution composed of sodium hydroxide, sodium carbonate, and nonionic surfactant. The mass fraction of sodium hydroxide in the solution is 3%, the mass fraction of sodium carbonate is 2%, and the mass fraction of nonionic surfactant is 0.5%. Control the solution temperature at 35℃, turn on low-speed stirring at 100r / min, and soak at a constant temperature for 10min. After soaking, rinse with deionized water in three stages of countercurrent rinsing until the pH value of the rinsing water is stable at 6.8.

[0054] S3. Send the rinsed substrate into a hot air circulating drying oven, control the drying temperature at 65℃, the circulating air speed at 3m / s, and the relative humidity at 20%, and continue drying for 15 minutes. Check the substrate moisture content every 5 minutes to keep the substrate moisture content at 2.8% to obtain a clean and dry coating substrate.

[0055] S4. Weigh 100 parts of waterborne polyurethane emulsion with a solid content of 30%, 8 parts of hydroxyl silicone oil waterproofing agent, 5 parts of chitosan quaternary ammonium salt antifungal agent, 1 part of polyether modified organosilicon leveling agent, 2 parts of aziridine crosslinking agent, and 25 parts of deionized water. Add all raw materials to the stirred reactor in sequence and stir at a low speed of 300 r / min for 15 min to obtain the coating mixture base material.

[0056] S5. Transfer the coating mixture to a high-speed shear disperser, control the dispersion speed at 1000 r / min and the dispersion temperature at 20℃, disperse at high speed for 10 min, and after dispersion, use a 10μm microporous filter device for pressure filtration at a filtration pressure of 0.2 MPa to obtain a moisture-proof and mildew-proof coating liquid with a particle fineness of less than 10μm.

[0057] S6. Vertically immerse the dried substrate into the coating solution in a Class 10,000 clean, sealed immersion tank. The temperature of the coating solution is kept constant at 25°C. Control the immersion time to 3 minutes to allow the substrate fibers to fully absorb the coating solution. Then, vertically lift the substrate at a uniform speed of 0.6 m / min to control the wet film thickness of the coating to 35 μm, ensuring uniform coating adhesion without any missed areas or drips.

[0058] S7. Place the dip-coated substrate into a low-temperature pre-baking oven and heat it to 45°C at a rate of 5°C / min. Pre-bake for 5 minutes to remove free moisture from the coating surface. Then transfer it to a hot air curing oven and heat it to 115°C at a rate of 8°C / min. Heat cure for 10 minutes to complete the cross-linking film formation reaction of the coating.

[0059] S8. Remove the heat-cured nonwoven bag from the curing oven and allow it to cool naturally at room temperature for 20 minutes until the product temperature drops below 25°C. After passing the appearance and coating adhesion tests, the finished moisture-proof and mildew-proof nonwoven bag is obtained.

[0060] Example 2

[0061] S1. A high-pressure clean air blowing device is used to perform all-round surface purification treatment on the polypropylene non-woven bag substrate. The blowing air pressure is controlled at 0.45MPa, the blowing air velocity is 20m / s, and the blowing is continued for 7 minutes to remove floating dust, loose fibers and mechanical impurities from the substrate surface, thus completing the substrate purification pretreatment.

[0062] S2. Immerse the pretreated nonwoven bag substrate in an alkaline degreasing solution composed of sodium hydroxide, sodium carbonate, and nonionic surfactant. The mass fraction of sodium hydroxide in the solution is 4%, the mass fraction of sodium carbonate is 3.5%, and the mass fraction of nonionic surfactant is 0.7%. Control the solution temperature at 42℃, turn on low-speed stirring at 150r / min, and soak at a constant temperature for 17min. After soaking, use deionized water for three-stage countercurrent rinsing until the pH value of the rinsing water stabilizes at 7.0.

[0063] S3. Send the rinsed substrate into a hot air circulating drying oven, control the drying temperature at 75℃, the circulating air speed at 5m / s, and the relative humidity at 25%, and continue drying for 25 minutes. Check the substrate moisture content every 5 minutes to keep the substrate moisture content at 2.5% to obtain a clean and dry coating substrate.

[0064] S4. Weigh 100 parts of waterborne polyurethane emulsion with a solid content of 35%, 10 parts of hydroxyl silicone oil waterproofing agent, 7 parts of chitosan quaternary ammonium salt antifungal agent, 1.5 parts of polyether modified organosilicon leveling agent, 2.5 parts of aziridine crosslinking agent, and 30 parts of deionized water. Add all raw materials to the stirred reactor in sequence and stir at a low speed of 400 r / min for 18 min to obtain the coating mixture base material.

[0065] S5. Transfer the coating mixture to a high-speed shear disperser, control the dispersion speed at 1900 r / min and the dispersion temperature at 25℃, disperse at high speed for 15 min, and after dispersion, use a 10μm microporous filter device for pressure filtration at a filtration pressure of 0.25 MPa to obtain a moisture-proof and mildew-proof coating liquid with a particle fineness of less than 10μm.

[0066] S6. Vertically immerse the dried substrate into the coating solution in a Class 10,000 clean, sealed immersion tank. The temperature of the coating solution is kept constant at 25°C. Control the immersion time to 5 minutes to allow the substrate fibers to fully absorb the coating solution. Then, vertically lift the substrate at a uniform speed of 1.2 m / min to control the wet film thickness of the coating to 55 μm, ensuring uniform coating adhesion without any missed areas or drips.

[0067] S7. Place the dip-coated substrate into a low-temperature pre-baking oven and heat it to 55°C at a uniform rate of 5°C / min for 8 minutes to remove free moisture from the coating surface. Then transfer it to a hot air curing oven and heat it to 130°C at a uniform rate of 8°C / min for 15 minutes to complete the cross-linking film formation reaction of the coating.

[0068] S8. Remove the heat-cured nonwoven bag from the curing oven and allow it to cool naturally at room temperature for 25 minutes until the product temperature drops below 25°C. After passing the appearance and coating adhesion tests, the finished moisture-proof and mildew-proof nonwoven bag is obtained.

[0069] Example 3

[0070] S1. A high-pressure clean air blowing device is used to perform all-round surface purification treatment on the polypropylene non-woven bag substrate. The blowing air pressure is controlled at 0.6MPa and the blowing air velocity is 25m / s. The blowing is continued for 10 minutes to remove floating dust, loose fibers and mechanical impurities from the substrate surface, thus completing the substrate purification pretreatment.

[0071] S2. Immerse the pretreated nonwoven bag substrate in an alkaline degreasing solution composed of sodium hydroxide, sodium carbonate, and nonionic surfactant. The mass fraction of sodium hydroxide in the solution is 5%, the mass fraction of sodium carbonate is 5%, and the mass fraction of nonionic surfactant is 1%. Control the solution temperature at 50℃, turn on low-speed stirring at 200r / min, and soak at a constant temperature for 25min. After soaking, use deionized water for three-stage countercurrent rinsing until the pH value of the rinsing water stabilizes at 7.2.

[0072] S3. The rinsed substrate is sent into a hot air circulating drying oven, and the drying temperature is controlled at 85℃, the circulating air speed is 8m / s, the relative humidity is controlled at 30%, and the drying is continued for 35 minutes. The moisture content of the substrate is checked every 5 minutes. The final moisture content of the substrate is controlled at 2.2%, and a clean and dry coating substrate is obtained.

[0073] S4. Weigh 100 parts of waterborne polyurethane emulsion with a solid content of 40%, 12 parts of hydroxyl silicone oil waterproofing agent, 9 parts of chitosan quaternary ammonium salt antifungal agent, 2 parts of polyether modified organosilicon leveling agent, 3 parts of aziridine crosslinking agent, and 35 parts of deionized water. Add all raw materials to the stirred reactor in sequence and stir at a low speed of 500 r / min for 20 min to obtain the coating mixture base material.

[0074] S5. Transfer the coating mixture to a high-speed shear disperser, control the dispersion speed at 2800 r / min and the dispersion temperature at 30℃, disperse at high speed for 20 min, and after dispersion, use a 10μm microporous filter device for pressure filtration at a filtration pressure of 0.3MPa to obtain a moisture-proof and mildew-proof coating liquid with a particle fineness of less than 10μm.

[0075] S6. Vertically immerse the dried substrate into the coating solution in a Class 10,000 clean, sealed immersion tank. The temperature of the coating solution is kept constant at 25°C. Control the immersion time to 7 minutes to allow the substrate fibers to fully absorb the coating solution. Then, vertically lift the substrate at a uniform speed of 1.8 m / min to control the wet film thickness of the coating to 75 μm, ensuring uniform coating adhesion without any missed areas or drips.

[0076] S7. Place the dip-coated substrate into a low-temperature pre-baking oven and heat it to 65°C at a uniform rate of 5°C / min for 12 minutes to remove free moisture from the coating surface. Then transfer it to a hot air curing oven and heat it to 145°C at a uniform rate of 8°C / min for 20 minutes to complete the cross-linking film formation reaction of the coating.

[0077] S8. Remove the heat-cured nonwoven bag from the curing oven and allow it to cool naturally at room temperature for 30 minutes until the product temperature drops below 25°C. After passing the appearance and coating adhesion tests, the finished moisture-proof and mildew-proof nonwoven bag is obtained.

[0078] Comparative Example 1

[0079] S1. A high-pressure clean air blowing device is used to clean the surface of the polypropylene nonwoven bag substrate. The blowing air pressure is controlled at 0.3MPa and the blowing air velocity is 15m / s. The blowing is continued for 5 minutes to remove floating dust and loose fibers from the substrate surface.

[0080] S2. Immerse the pretreated non-woven bag substrate in clean water at room temperature for 10 minutes, then remove and drain naturally without alkaline degreasing or three-stage countercurrent rinsing.

[0081] S3. The drained substrate is placed in a room temperature environment to air dry naturally without controlling the temperature, wind speed and humidity. The final moisture content of the substrate is higher than 8%, which does not meet the standard for clean and dry coating.

[0082] S4. Weigh 100 parts of ordinary water-based acrylic emulsion, 5 parts of industrial waterproof coating, 3 parts of ordinary mildew inhibitor, and 40 parts of deionized water. Mix them and stir at 200 r / min for 10 min to obtain an ordinary coating mixture without adding waterproof agent, crosslinking agent, or special leveling agent.

[0083] S5. The ordinary coating mixture is dispersed by low-speed stirring at 500 r / min without high-speed shearing and microfiltration. As a result, the coating liquid exhibits particle agglomeration and stratification.

[0084] S6. The naturally air-dried substrate is immersed in a common coating mixture and coated at room temperature for 1 minute. It is then rapidly lifted at 3 m / min. The wet film thickness of the coating is uneven and there is no standardized thickness control.

[0085] S7. Place the dip-coated substrate directly at room temperature to air dry naturally, without low-temperature pre-baking or segmented heat curing treatment, and the coating will not undergo cross-linking film formation reaction.

[0086] S8. The dried non-woven bags are used directly as finished products without cooling or performance testing, resulting in non-woven bags processed using traditional methods.

[0087] Table 1 Comparison of core process parameters between Examples 1-3 and Comparative Example 1

[0088] Purge pressure / MPa 0.3 0.45 0.6 0.3 Degreasing temperature / ℃ 35 42 50 normal temperature Moisture content after drying / % 2.8 2.5 2.2 ＞8 <![CDATA[High-speed dispersion rotation speed / r・min -1 > 1000 1900 2800 500 Dipping time / min 3 5 7 1 Pre-drying temperature / ℃ 45 55 65 none Thermosetting temperature / °C 115 130 145 none Coating crosslinking reaction have have have none

[0089] Explanation of the table: This table fully presents the differences in core process parameters between Examples 1-3 and Comparative Example 1. Examples 1-3 strictly follow the process requirements of this invention, completing the entire process of substrate purification, degreasing, drying, coating compounding, dispersion, dip coating, and segmented curing. All parameters are within the defined range, and the process conditions are optimized synchronously with formula adjustments, fully triggering the hydrolysis, crosslinking, coordination, and copolymerization reactions of the coating. Comparative Example 1 uses a traditional, extensive process, lacking key steps such as degreasing, precise drying, high-speed dispersion, and segmented curing. No coating crosslinking reaction occurs, and the process parameters are not standardized. The table intuitively demonstrates the refined, standardized, and controllable process advantages of this invention, verifying the completeness and innovation of the process of this invention.

[0090] Table 2 Comparison of Product Performance between Examples 1-3 and Comparative Example 1

[0091] Coating adhesion excellent Excellent Excellent Difference Moisture barrier good excellent Excellent Difference Long-lasting anti-mildew properties good excellent Excellent none abrasion resistance excellent Excellent Excellent Difference Substrate breathability intact intact intact decline

[0092] Explanation of the table: This table compares the core application performance of the products prepared in Examples 1-3 with those in Comparative Example 1. Examples 1-3, due to their multi-component compound coating and segmented cross-linking curing process, exhibit strong coating adhesion, progressively improved moisture and mildew resistance, excellent abrasion resistance, and complete preservation of the non-woven bag's breathability. All performance characteristics meet the standards for environmentally friendly packaging materials. Example 3, with its optimal raw material ratio and most stringent process parameters, achieves the best overall performance. Comparative Example 1, due to missing processes and lack of cross-linking molding of the coating, suffers from extremely poor adhesion, moisture resistance, mildew resistance, and abrasion resistance, failing to meet the requirements for long-term use. The table fully verifies that the process of this invention can significantly improve the comprehensive protective performance of non-woven bags, overcome the technical defects of traditional processes, and possess significant technological advancements and industrial application value.

[0093] refer to Figure 2This bar chart visually presents the differences in coating adhesion among the four groups of samples, and the numerical results highly match the process logic of this invention. Examples 1-3, after completing the full process, achieved a stable bond between the coating and the nonwoven fibers, with high adhesion scores, which gradually improved with optimized process parameters. Example 3, due to its optimal formulation and stringent process control, achieved peak adhesion. Comparative Example 1, lacking the crucial steps of degreasing and cross-linking curing, had its coating simply adhere to the substrate surface, resulting in significantly deteriorated adhesion, with a score of only 3.1. This chart clearly verifies that substrate pretreatment and thermal cross-linking are the core of improving coating adhesion. A refined process allows the coating to firmly adhere to the fibers, preventing peeling and flaking, while traditional, extensive processes cannot meet the bonding strength requirements of the protective coating, providing intuitive data support for process optimization.

[0094] refer to Figure 3 This line graph reflects the direct impact of substrate moisture content on the moisture-proof performance of the coating, and the numerical trend aligns with the design principles of the drying process of this invention. In Examples 1-3, the substrate moisture content was strictly controlled below 3%. The lower the moisture content, the more fully the coating liquid and fibers bond, resulting in a denser, cross-linked coating and improved moisture-proof efficiency. At a moisture content of 2.2%, the moisture-proof efficiency reached 94%. When the moisture content exceeded the process control range, residual moisture inside the fibers damaged the cross-linked structure of the coating, leading to porosity and cracking, and a rapid decline in moisture-proof efficiency, reaching only 30% at 8% moisture content. This graph visually demonstrates the necessity of the hot air circulation drying process of this invention. Precise control of the substrate moisture content is a key prerequisite for ensuring the moisture-proof performance of the coating and provides a clear data standard for moisture content control during production.

[0095] refer to Figure 4 This radar chart comprehensively compares the core performance of the optimal embodiment and the comparative example, clearly demonstrating the comprehensive advantages of the process of this invention. Example 2, through a complete coating compounding, cross-linking reaction, and segmented curing process, achieves high scores in all four core protective properties: adhesion, moisture resistance, mildew resistance, and abrasion resistance, while fully preserving the breathability of the substrate, achieving a balance between protection and practicality. Comparative Example 1, lacking a key process, has extremely poor performance in all four protective properties, with only slightly better breathability, failing to meet the requirements for moisture and mildew prevention. The performance outline of Example 2 in the chart is full and balanced, while the outline of Comparative Example 1 is severely incomplete, intuitively verifying that this invention, through multi-component cross-linking, coordination reaction, and refined temperature control, can simultaneously improve the multiple protective properties of non-woven bags, solving the defects of traditional processes such as single performance and protective failure, fully demonstrating the practicality and advancement of the process of this invention.

[0096] refer to Figure 5This scatter plot reveals the influence of thermosetting temperature on coating density, and the data results match the parameter design of the segmented thermosetting process of this invention. Under room temperature and low-temperature curing conditions, the coating cannot undergo sufficient cross-linking and copolymerization reactions, resulting in a loose structure with many pores and extremely low density. As the temperature increases to the process range of 115℃-145℃ in this invention, the water-based polyurethane, silicone, and cross-linking agent in the coating react fully to form a three-dimensional interpenetrating network structure, and the density rapidly increases and tends to stabilize, reaching a peak at 145℃. Temperatures exceeding the optimal range will lead to thermal damage to the coating, while temperatures below the range will result in incomplete reactions. This scatter plot visually verifies the scientific validity of the 115℃-145℃ thermosetting temperature range of this invention. Precise temperature control allows the coating to form a continuous and dense structure, fundamentally improving the moisture-proof and mildew-proof effect, and providing intuitive data for setting curing parameters in production.

[0097] 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 process for preparing a moisture and mildew resistant coating for nonwoven bags, characterized by, Includes the following steps: S1. An air blowing device is used to perform all-round surface purification treatment on the non-woven bag substrate to complete the purification pretreatment of the substrate. S2. Immerse the pretreated nonwoven bag substrate in an alkaline degreasing solution composed of sodium hydroxide, sodium carbonate and nonionic surfactant. After immersion, rinse with deionized water in three stages of countercurrent rinsing until the pH of the rinsing water is stable at 6.8-7.

2. S3. Place the rinsed non-woven bag substrate into a hot air circulating drying oven and dry continuously for 15-35 minutes. S4. Weigh out waterborne polyurethane emulsion, hydroxyl silicone oil waterproofing agent, chitosan quaternary ammonium salt mildew inhibitor, polyether modified organosilicon leveling agent, aziridine crosslinking agent and deionized water according to the mass fractions of 30%-40% solid content, add the above raw materials to the stirred reaction vessel in sequence, and stir to obtain the coating mixture base material. S5. Transfer the coating mixture into a high-speed shear disperser, disperse at a temperature of 20℃-30℃ for 10-20 minutes, so that the particle size of the mixture is less than 10μm, and obtain a moisture-proof and mildew-proof coating liquid. S6. Vertically immerse the dried non-woven bag substrate into the moisture-proof and mildew-proof coating liquid, control the immersion time to be 3min-7min, and then vertically lift it at a uniform speed of 0.6m / min-1.8m / min, control the wet film thickness of the coating to be 35μm-75μm. S7. First, put the non-woven bag substrate that has been dipped into the low temperature pre-drying oven, control the temperature at 45℃-65℃, pre-dry for 5min-12min, and then transfer it into the hot air curing oven, control the temperature at 115℃-145℃, and heat cure for 10min-20min. S8. Remove the heat-cured nonwoven bag from the curing oven and allow it to cool naturally at room temperature for 20-30 minutes until the product temperature drops below 25°C. After passing the appearance and coating adhesion tests, the finished moisture-proof and mildew-proof nonwoven bag is obtained.

2. The preparation process of the moisture-proof and mildew-proof coating for nonwoven bags according to claim 1, characterized in that, This also includes fine-tuning the pH of the moisture-proof and mildew-proof coating solution after it has been prepared, controlling the pH of the system between 5.5 and 7.0 to trigger the hydrolysis and condensation reaction of the hydroxyl silicone oil waterproofing agent.

3. The preparation process of the moisture-proof and mildew-proof coating for nonwoven bags according to claim 1, characterized in that, It also includes the use of a high-temperature environment to trigger a cross-linking film-forming reaction between the aziridine cross-linking agent and the hydroxyl and carboxyl groups on the waterborne polyurethane molecular chain during the thermosetting process.

4. The preparation process of the moisture-proof and mildew-proof coating for non-woven bags according to claim 1, characterized in that, The mass fractions of each component in the alkaline degreasing solution in S2 are 3%-5% sodium hydroxide, 2%-5% sodium carbonate, and 0.5%-1% nonionic surfactant, with a total mass fraction of 5%-12%. During the soaking process, a low-speed stirring device is used to drive the solution flow and improve the degreasing effect. The stirring speed is 100r / min-200r / min.

5. The preparation process of the moisture-proof and mildew-proof coating for nonwoven bags according to claim 1, characterized in that, The relative humidity of the hot air circulating drying oven in S3 is controlled at 20%-30%. The moisture content of the substrate is checked every 5 minutes during the drying process to keep the moisture content of the substrate stable below 3%.

6. The process for preparing the moisture-proof and mildew-proof coating on nonwoven bags according to claim 1, characterized in that, It also includes coordinating and inhibiting the bacteria by reacting chitosan quaternary ammonium salt antifungal agent with zinc ions in the system during the preparation of the coating mixture base material.

7. The process for preparing the moisture-proof and mildew-proof coating on nonwoven bags according to claim 1, characterized in that, In S6, the dip coating process is carried out in a clean and sealed dip coating tank. The cleanliness of the internal environment of the dip coating tank reaches Class 10,000, the temperature of the coating liquid is kept constant at 25°C, and the substrate is kept vertical and without tilting during the lifting process.

8. The process for preparing the moisture-proof and mildew-proof coating on nonwoven bags according to claim 1, characterized in that, The S7 low-temperature pre-baking and heat curing processes adopt a segmented temperature control mode. During the pre-baking stage, the temperature is increased at a uniform rate of 5℃ / min, and during the heat curing stage, the temperature is increased at a uniform rate of 8℃ / min.

9. The process for preparing the moisture-proof and mildew-proof coating on nonwoven bags according to claim 1, characterized in that, After the high-speed shear dispersion treatment in S5 is completed, the moisture-proof and mildew-proof coating liquid is pressurized and filtered using a microporous filtration device with a precision of 10μm.

10. The process for preparing the moisture-proof and mildew-proof coating on nonwoven bags according to claim 1, characterized in that, It also includes a copolymerization reaction between the silicone molecules inside the coating and the waterborne polyurethane molecules after thermosetting.

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