High waterproof and environment-friendly packaging carton and preparation method thereof

Abstract

The application relates to the field of packaging cartons, in particular to a high-waterproof environment-friendly packaging carton material and a preparation method thereof. The high-waterproof environment-friendly packaging carton material comprises a paperboard layer and a waterproof antibacterial layer coated on the surface of the paperboard layer, the thickness of the waterproof antibacterial layer is 30-50 microns, the waterproof antibacterial layer is prepared by spraying waterproof antibacterial paint on the surface of the paperboard layer and solidifying, wherein the waterproof antibacterial paint comprises the following preparation raw materials in mass fractions: modified water-based polyurethane emulsion 100-110 parts, carboxymethyl chitosan 3-5 parts, modified polylactic acid 8-10 parts, composite antibacterial agent 1-2 parts and silane coupling agent 0.5-0.8 parts, the composite antibacterial agent is composed of modified silver cerium doped titanium dioxide and peppermint oil. The high-waterproof environment-friendly packaging carton material of the application combines multiple functions such as waterproof, antibacterial, flame-retardant, environment-friendly safety and the like, has good mechanical properties and durability, is very suitable for the demand of the food packaging industry, and has a wide market application prospect.

Description

Technical Field

[0001] This application relates to the field of packaging paper boxes, and in particular to a highly waterproof and environmentally friendly packaging paper box material and its preparation method. Background Technology

[0002] As a crucial component of logistics and commodity circulation, the performance of packaging boxes is vital to product protection and environmental impact. With increasing environmental awareness, the market is placing higher demands on the environmental performance of packaging boxes. Simultaneously, in humid or rainy areas, the waterproof performance of packaging boxes is particularly important. However, existing packaging boxes often struggle to simultaneously meet both high waterproof and environmental protection requirements.

[0003] For example, paper packaging boxes used in the catering industry need to have good waterproof, oil-proof, and antibacterial properties. Existing paper packaging boxes usually have fluorinated oil-proof and water-proof agents added to improve their waterproof and oil-proof properties, but these contain trace amounts of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which pose a risk of being transferred into the human body with food, which is detrimental to food safety and human health. In addition, paper packaging boxes are also flammable. How to improve the waterproof, oil-proof, antibacterial, and flame-retardant properties of paper packaging boxes is also a research hotspot in this field. Summary of the Invention

[0004] The purpose of this application is to address the shortcomings of current technology by providing a highly waterproof and environmentally friendly packaging paper box material and its preparation method. The preparation method of the highly waterproof and environmentally friendly packaging paper box material of this application is simple to manufacture and low in cost. At the same time, the highly waterproof and environmentally friendly packaging paper box material has excellent hydrophobic properties, antibacterial properties, flame retardancy and environmental safety, meeting the needs of the food packaging industry.

[0005] In the first aspect, this application provides a highly waterproof and environmentally friendly packaging paper box material, which adopts the following technical solution: A highly waterproof and environmentally friendly packaging paper box material includes a cardboard layer and a waterproof and antibacterial layer coated on the surface of the cardboard layer. The thickness of the waterproof and antibacterial layer is 30-50 micrometers. The waterproof and antibacterial layer is obtained by spraying a waterproof and antibacterial coating onto the surface of the cardboard layer and curing it. The waterproof and antibacterial coating, by weight, includes the following raw materials: 100-110 parts of modified waterborne polyurethane emulsion, 3-5 parts of carboxymethyl chitosan, 8-10 parts of modified polylactic acid, 1-2 parts of composite antibacterial agent, and 0.5-0.8 parts of silane coupling agent. The composite antibacterial agent is composed of modified silver-cerium-doped titanium dioxide and peppermint oil.

[0006] By adopting the above technical solutions, the modified waterborne polyurethane emulsion, as the main component of the waterproof and antibacterial coating, introduces dihydroxybutyl polydimethylsilane through fine emulsion polymerization, improving the compatibility between the polyurethane chain and the polyacrylate chain and reducing the degree of phase separation. This modification not only enhances the waterproof, oil-proof, and flexible properties of the material but also endows the packaging paperboard material with high self-healing properties. Carboxymethyl chitosan effectively improves the antibacterial and oil-repellent properties of the packaging paperboard material. Carboxymethyl chitosan is a natural polymer compound with good biocompatibility and biodegradability, making it important for applications in environmentally friendly materials. Modified polylactic acid (PLA): PLA is an environmentally friendly polymer material, but it is brittle and has poor aging resistance. In this application, a composite phytate is synthesized through citrulline, phytic acid, and genipin, and then modified with tannic acid to improve its toughening effect. The addition of tannic acid and composite phytate effectively improves the flame retardancy of the waterproof and antibacterial layer. Furthermore, the tannic acid introduced into the modified polylactic acid undergoes a free radical grafting reaction with sodium alginate in carboxymethyl chitosan, enhancing the complexity of the waterproof and antibacterial layer network structure, improving the performance uniformity of the waterproof and antibacterial coating, and increasing its adhesion to the cardboard layer, thus extending its service life. Composite antibacterial agent (modified silver-cerium-doped titanium dioxide and peppermint oil): Modified silver-cerium-doped titanium dioxide possesses excellent antibacterial properties, photocatalytic performance, and dispersibility, and exhibits good compatibility with other components of the waterproof and antibacterial coating. Peppermint oil, as a natural antibacterial agent, works synergistically with modified silver-cerium-doped titanium dioxide to provide a good antibacterial effect. Silane coupling agent: As a crosslinking agent, it enhances the interaction between different components, strengthens the adhesion between the coating and the cardboard layer, and ensures the stability and durability of the coating. In summary, the highly waterproof and environmentally friendly packaging paper box material of this application, through the synergistic effect of its components, not only achieves excellent hydrophobic, antibacterial, and flame-retardant properties, but also takes into account environmental protection and safety, meeting the high standards required by the food packaging industry.

[0007] Preferably, the mass ratio of the modified silver-cerium-doped titanium dioxide to the peppermint oil is 3:2.

[0008] By employing the above-mentioned technical solutions, modified silver-cerium-doped titanium dioxide exhibits excellent antibacterial properties. Both silver and cerium ions are known potent antibacterial agents; they can inhibit bacterial growth and reproduction by disrupting the cell walls and membranes of bacteria. Titanium dioxide is a commonly used photocatalyst that generates free radicals under ultraviolet light irradiation. These free radicals can decompose organic matter, thereby achieving antibacterial and self-cleaning functions. The doping of silver and cerium further enhances the photocatalytic activity of titanium dioxide, enabling it to function in the visible light range as well. Modified silver-cerium-doped titanium dioxide exhibits good dispersibility, which helps it to be uniformly distributed in waterproof and antibacterial coatings, ensuring consistent antibacterial performance throughout the coating. Peppermint oil contains various compounds with antibacterial activity, such as menthol, which can effectively inhibit or kill microorganisms. Peppermint oil has a refreshing aroma, which can add fragrance to packaging materials and enhance the user experience. Modified silver-cerium-doped titanium dioxide primarily targets bacteria, while the natural antibacterial components in peppermint oil can act on a variety of microorganisms, including bacteria and fungi. The combination of the two can broaden the antibacterial spectrum and improve the antibacterial effect. Compounds in peppermint oil can disrupt the cell membranes of microorganisms, increasing cell membrane permeability and allowing silver and cerium ions to more easily enter bacterial cells, thus enhancing the antibacterial effect. The photocatalytic properties of modified silver-cerium-doped titanium dioxide, combined with the chemical antibacterial effects of peppermint oil, can provide sustained antibacterial protection under various environmental conditions. In summary, the combined use of modified silver-cerium-doped titanium dioxide and peppermint oil in a 3:2 mass ratio not only provides broad-spectrum and highly effective antibacterial protection but also leverages their respective properties to synergistically enhance the overall antibacterial effect, while simultaneously bringing additional functionality and user experience to packaging materials.

[0009] Preferably, the material of the cardboard layer is one of paper bag paper, kraft paper, kraft cardboard, linerboard, and corrugated paper.

[0010] Preferably, the thickness of the cardboard layer is 200-400 micrometers.

[0011] Preferably, the preparation method of the modified waterborne polyurethane emulsion includes the following steps: S51. According to the mass fractions, 71 parts of dihydroxybutyl polydimethylsilane, 114 parts of butyl acrylate, 61 parts of styrene, 89 parts of polycaprolactone, 33 parts of isophorone diisocyanate, 3 parts of hydroxyethyl methacrylate, 1.8 parts of azobisisobutyronitrile, 0.5 parts of dibutyltin dilaurate, and 10.5 parts of n-hexadecane are mixed evenly to obtain a mixture; S52. The mixture is added to 300 parts of an emulsifier aqueous solution with a mass concentration of 6%, and then pre-emulsified at 3000 r / min to obtain a crude emulsion. The crude emulsion is then ultrasonically treated in an ice-water bath using a cell disruptor for 40 min to obtain a monomer fine emulsion. Finally, the obtained monomer fine emulsion is stirred in a nitrogen atmosphere for 1.5 h, then transferred to a three-necked flask and subjected to a fine emulsion polymerization reaction at a temperature of 72℃ in a nitrogen atmosphere for 10 h to obtain a modified waterborne polyurethane emulsion.

[0012] By employing the above technical solution, the preparation method of this application successfully introduces dihydroxybutyl polydimethylsilane into the polyurethane chain segment via fine emulsion polymerization, obtaining a modified waterborne polyurethane emulsion. This method not only improves the compatibility between the polyurethane chain and the polyacrylate chain but also reduces the degree of phase separation, thereby enhancing the waterproof, oil-resistant, and flexible properties of the waterproof and antibacterial layer. Simultaneously, by introducing hydrophobic dihydroxybutyl polydimethylsilane, it effectively inhibits water and oil molecules from penetrating from the surface of the highly waterproof and environmentally friendly packaging paperboard material into the interior, further improving its waterproof performance.

[0013] Preferably, the emulsifier is 1-allyloxy-3-4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate.

[0014] Preferably, the preparation method of the modified silver-cerium-doped titanium dioxide includes the following steps: S71. At room temperature, add 100 mL of tetrabutyl titanate to a solution consisting of 160 mL of ethanol and 30 mL of deionized water, and stir for 30 min to form solution A. S72. Add 1.5g of silver nitrate and 12g of cerium nitrate to a solution consisting of 100mL of ethanol, 15mL of acetic acid and 45mL of water to form solution B; S73. Add solution B dropwise to solution A, stir for 60 min, heat to 42℃, let stand and age for 12 h, then centrifuge, wash, and dry at 80℃ for 12 h to obtain silver cerium doped titanium dioxide. S74. Mix 0.8g of γ-(methacryloyloxy)propyltrimethoxysilane with 70g of ethanol and 8g of water, and hydrolyze for 4h to obtain mixture C; S75. Add the obtained silver-cerium-doped titanium dioxide to mixture C, then heat to 43℃, stir at 300r / min for 250min, finally filter, wash, dry at 85℃ and grind to obtain modified silver-cerium-doped titanium dioxide with an average particle size of 40 nanometers.

[0015] By employing the above-mentioned technical solutions, modified silver-cerium-doped titanium dioxide exhibits excellent antibacterial properties. Both silver and cerium ions are known potent antibacterial agents; they can inhibit bacterial growth and reproduction by disrupting bacterial cell walls and membranes. Titanium dioxide is a commonly used photocatalyst; under ultraviolet light irradiation, it can generate free radicals that can decompose organic matter, achieving antibacterial and self-cleaning functions. The doping of silver and cerium further enhances the photocatalytic activity of titanium dioxide, enabling it to function in the visible light range. Modified silver-cerium-doped titanium dioxide exhibits good dispersibility, which helps it to be uniformly distributed in waterproof and antibacterial coatings, ensuring consistent antibacterial properties throughout the coating. Modified silver-cerium-doped titanium dioxide shows good compatibility with other components in waterproof and antibacterial coatings and can synergistically work with other components such as modified waterborne polyurethane emulsions and carboxymethyl chitosan to jointly improve the waterproof, antibacterial, and flame-retardant properties of the coating. In summary, modified silver-cerium-doped titanium dioxide plays a key role in highly waterproof and environmentally friendly packaging paperboard materials due to its antibacterial properties, photocatalytic properties, and good dispersibility. It also works synergistically with other components to improve the overall performance of the material.

[0016] Preferably, the silane coupling agent is composed of isopropyltrioleoyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane in a mass ratio of 3:4.

[0017] By employing the above technical solution, the main function of the silane coupling agent is as a crosslinking agent, enhancing the adhesion between different materials. In this material, it effectively improves the bonding force between the waterproof and antibacterial coating and the cardboard layer, ensuring that the coating adheres firmly to the cardboard and is not easily peeled off. Isopropyltrioleoyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane are both hydrophobic compounds, which can reduce the permeability of water molecules to the coating, thereby enhancing the overall water resistance of the material. By promoting the formation of chemical bonds between the coating and the cardboard, the silane coupling agent helps to enhance the mechanical strength of the coating, such as abrasion resistance and impact resistance. The silane coupling agent can also improve the aging resistance of the material and extend the service life of the packaging box. Isopropyltrioleoyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane each have different functional groups; the oleoyloxy group of the former and the methacryloyloxy group of the latter can react with different material surfaces to form strong chemical bonds. Isopropyltrioleoyloxytitanate exhibits strong hydrophobicity, while γ-(methacryloyloxy)propyltrimethoxysilane possesses certain hydrophilicity. This combination helps form a balanced interface between the coating and the paperboard, effectively repelling moisture while ensuring good adhesion between the coating and the paperboard. Both exhibit good chemical stability, maintaining their chemical structure under various environments, thus ensuring the stability and durability of the coating. By adjusting the ratio of the two silane coupling agents, the compatibility of the coating-paperboard interface can be optimized, achieving the best adhesion effect. In summary, the use of silane coupling agents not only improves the overall performance of the material but also optimizes the bonding between the coating and the paperboard through the synergistic effect of their components, enhancing the material's water resistance, mechanical properties, and aging resistance, while maintaining environmentally friendly characteristics, meeting the needs of the food packaging industry.

[0018] Preferably, the method for preparing the modified polylactic acid includes the following steps: S91. According to the mass fraction, 131 parts of 70% phytic acid solution, 4.6 parts of citrulline, and 0.3 parts of genipin are mixed, heated to 88℃ and kept at that temperature for 5 hours, purified with ethanol, filtered, and dried to obtain phytic acid complex salt. S92. According to the mass fraction, mix 10 parts of tannic acid and 90 parts of phytic acid composite salt, add 900 parts of polylactic acid, and mix in a high-speed mixer to obtain modified polylactic acid.

[0019] By adopting the above technical solution, the toughness of polylactic acid (PLA) can be effectively improved by adding a modifier composed of tannic acid and phytic acid composite salts. This is because tannic acid and phytic acid composite salts can act as plasticizers, increasing the mobility between polymer chains and thus reducing the brittleness of the material. Tannic acid and phytic acid composite salts can also function as flame retardants in the material. Tannic acid, in particular, is a natural flame retardant that can improve the thermal stability and flame retardancy of the material. The phytic acid composite salts in the modified PLA have good water resistance, which helps to improve the overall waterproof performance of the material. The tannic acid in the modified PLA undergoes a free radical grafting reaction with sodium alginate in carboxymethyl chitosan. This chemical reaction enhances the interaction between different layers and improves interlayer adhesion. The grafting reaction increases the complexity of the internal structure of the material, forming a more stable network structure, which not only improves the overall performance of the material but also helps to evenly distribute applied pressure or impact. Due to the above-mentioned characteristics of modified PLA, it can effectively extend the service life of packaging boxes, especially in resisting environmental factors (such as water and fire) and wear during use. In conclusion, the introduction of modified polylactic acid not only improves the physical and chemical properties of packaging cartons, but also optimizes the overall function of the material through synergistic effects with other components, making it more suitable for the needs of the food packaging industry.

[0020] Secondly, this application provides a method for preparing a highly waterproof and environmentally friendly packaging paper box material, using the following technical solution: As a general technical concept, this application also provides a method for preparing the above-mentioned highly waterproof and environmentally friendly packaging paper box material, including the following steps: S101. According to the mass parts, the modified waterborne polyurethane emulsion, carboxymethyl chitosan, modified polylactic acid, composite antibacterial agent and silane coupling agent are stirred evenly to obtain a waterproof antibacterial coating. S102. Spray the waterproof and antibacterial coating onto the surface of the cardboard layer, and then dry it at 80-85℃ for 60-70 minutes. A waterproof layer is formed through the drying and curing process to obtain a highly waterproof and environmentally friendly packaging paper box material.

[0021] In summary, the beneficial technical effects of this application are as follows: 1. Excellent hydrophobic properties: Through the preparation and application of modified waterborne polyurethane emulsions, the introduction of dihydroxybutyl polydimethylsilane significantly improves the hydrophobic properties of the material. This hydrophobic material can effectively prevent the penetration of moisture and oil, thereby protecting the contents of the packaging from contamination, and is particularly suitable for food packaging that requires moisture or oil protection.

[0022] 2. Excellent antibacterial and photocatalytic properties: The addition of carboxymethyl chitosan, modified silver-cerium-doped titanium dioxide, and peppermint oil enhances the antibacterial properties of the material. These antibacterial agents have the ability to disrupt bacterial cell walls, thereby inhibiting microbial growth, which is crucial for ensuring the hygiene and safety of food packaging. The photocatalytic properties of modified silver-cerium-doped titanium dioxide can be used to decompose organic matter, achieving a self-cleaning function, reducing maintenance costs, and extending service life.

[0023] 3. Improved flame retardancy: The combined effect of tannic acid and complex phytate enhances the material's flame retardant properties. In the event of a fire, this material burns more slowly, providing more time for rescue efforts and reducing the risk of fire.

[0024] 4. Improved durability: The introduction of modified polylactic acid (PLA) solves the problems of PLA's brittleness and poor aging resistance, increasing the material's flexibility and service life. This means that packaging materials can withstand pressure and impact during use and are less prone to breakage.

[0025] 5. Environmentally friendly: The materials used, such as polylactic acid, are biodegradable, aligning with current environmental trends. This helps reduce the environmental impact of plastic waste, meeting the goals of sustainable development.

[0026] 6. Cost-effectiveness: The simple and low-cost preparation method makes this material suitable for large-scale production. This not only reduces production costs but also makes environmentally friendly materials more readily accepted by the market.

[0027] 7. Self-healing properties: The material has high self-healing properties and can repair minor damage to a certain extent, which further enhances its durability and practicality. Detailed Implementation

[0028] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0029] Preparation Example 1: Preparation of Modified Waterborne Polyurethane Emulsion A method for preparing a modified waterborne polyurethane emulsion includes the following steps: S51. According to the mass fractions, 71g of hydroxybutylated polydimethylsilane, 114g of butyl acrylate, 61g of styrene, 89g of polycaprolactone, 33g of isophorone diisocyanate, 3g of hydroxyethyl methacrylate, 1.8g of azobisisobutyronitrile, 0.5g of dibutyltin dilaurate, and 10.5g of n-hexadecane are mixed evenly to obtain a mixture. S52. The mixture was added to 300g of 6% (w / w) aqueous solution of 1-allyloxy-3-4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate. The mixture was then pre-emulsified at 3000r / min to obtain a crude emulsion. The crude emulsion was then ultrasonically treated in an ice-water bath using a cell disruptor for 40min to obtain a monomer fine emulsion. Finally, the monomer fine emulsion was stirred in a nitrogen atmosphere for 1.5h and then transferred to a three-necked flask. The fine emulsion polymerization reaction was carried out at 72℃ in a nitrogen atmosphere for 10h to obtain a modified waterborne polyurethane emulsion.

[0030] Preparation Example 2: Preparation of Modified Silver-Cerium-Doped Titanium Dioxide The preparation method of modified silver-cerium-doped titanium dioxide includes the following steps: S71. At room temperature, add 100 mL of tetrabutyl titanate to a solution consisting of 160 mL of ethanol and 30 mL of deionized water, and stir for 30 min to form solution A. S72. Add 1.5g of silver nitrate and 12g of cerium nitrate to a solution consisting of 100mL of ethanol, 15mL of acetic acid and 45mL of water to form solution B; S73. Add solution B dropwise to solution A, stir for 60 min, heat to 42℃, let stand and age for 12 h, then centrifuge, wash, and dry at 80℃ for 12 h to obtain silver cerium doped titanium dioxide. S74. Mix 0.8g of γ-(methacryloyloxy)propyltrimethoxysilane with 70g of ethanol and 8g of water, and hydrolyze for 4h to obtain mixture C; S75. Add the obtained silver-cerium-doped titanium dioxide to mixture C, then heat to 43℃, stir at 300r / min for 250min, finally filter, wash, dry at 85℃ and grind to obtain modified silver-cerium-doped titanium dioxide with an average particle size of 40 nanometers.

[0031] Preparation Example 3: Preparation of Modified Polylactic Acid The preparation method of modified polylactic acid includes the following steps: S91. According to the mass fraction, 131g of 70% phytic acid solution, 4.6g of citrulline and 0.3g of genipin are mixed, heated to 88℃ and kept at that temperature for 5h, purified with ethanol, filtered and dried to obtain phytic acid complex salt. S92. According to the mass fraction, mix 10g of tannic acid and 90g of phytic acid composite salt, add 900g of polylactic acid, and mix in a high-speed mixer to obtain modified polylactic acid.

[0032] Preparation Example 1: Preparation of Waterborne Polyurethane Emulsion A method for preparing an aqueous polyurethane emulsion includes the following steps: S51. According to the mass fractions, 114g butyl acrylate, 61g styrene, 89g polycaprolactone, 33g isophorone diisocyanate, 3g hydroxyethyl methacrylate, 1.8g azobisisobutyronitrile, 0.5g dibutyltin dilaurate, and 10.5g n-hexadecane are mixed evenly to obtain a mixture. S52. The mixture was added to 300g of 6% (w / w) aqueous solution of 1-allyloxy-3-4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate. The mixture was then pre-emulsified at 3000r / min to obtain a crude emulsion. The crude emulsion was then ultrasonically treated in an ice-water bath using a cell disruptor for 40min to obtain a monomer fine emulsion. Finally, the monomer fine emulsion was stirred in a nitrogen atmosphere for 1.5h and then transferred to a three-necked flask. The fine emulsion polymerization reaction was carried out at 72℃ in a nitrogen atmosphere for 10h to obtain a modified waterborne polyurethane emulsion.

[0033] Example 1 A highly waterproof and environmentally friendly packaging paper box material includes a cardboard layer and a waterproof and antibacterial layer coated on the surface of the cardboard layer. The thickness of the waterproof and antibacterial layer is 30 micrometers. The waterproof and antibacterial layer is obtained by spraying a waterproof and antibacterial coating onto the surface of the cardboard layer and curing it. The waterproof and antibacterial coating, by mass parts, includes the following raw materials: 100g of modified waterborne polyurethane emulsion, 3g of carboxymethyl chitosan, 8g of modified polylactic acid, 1g of composite antibacterial agent, and 0.5g of silane coupling agent. The composite antibacterial agent is composed of modified silver-cerium-doped titanium dioxide and peppermint oil in a mass ratio of 3:2. The cardboard layer is a paper bag with a thickness of 400 micrometers. The silane coupling agent is composed of isopropyltrioleoyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane in a mass ratio of 3:4.

[0034] The above-mentioned method for preparing a highly waterproof and environmentally friendly packaging paper box material includes the following steps: S101. According to the mass parts, the modified waterborne polyurethane emulsion, carboxymethyl chitosan, modified polylactic acid, composite antibacterial agent and silane coupling agent are stirred evenly to obtain a waterproof antibacterial coating. S102. The waterproof and antibacterial coating is sprayed onto the surface of the cardboard layer, and then dried at 80°C for 70 minutes. A waterproof layer is formed through the drying and curing process, resulting in a highly waterproof and environmentally friendly packaging paper box material.

[0035] Example 2 A highly waterproof and environmentally friendly packaging paper box material includes a cardboard layer and a waterproof and antibacterial layer coated on the surface of the cardboard layer. The thickness of the waterproof and antibacterial layer is 50 micrometers. The waterproof and antibacterial layer is obtained by spraying a waterproof and antibacterial coating onto the surface of the cardboard layer and curing it. The waterproof and antibacterial coating, by mass parts, includes the following raw materials: 110g of modified waterborne polyurethane emulsion, 5g of carboxymethyl chitosan, 10g of modified polylactic acid, 2g of composite antibacterial agent, and 0.8g of silane coupling agent. The composite antibacterial agent is composed of modified silver-cerium-doped titanium dioxide and peppermint oil in a mass ratio of 3:2. The cardboard layer is kraft paper with a thickness of 200 micrometers. The silane coupling agent is composed of isopropyltrioleoyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane in a mass ratio of 3:4.

[0036] The above-mentioned method for preparing a highly waterproof and environmentally friendly packaging paper box material includes the following steps: S101. According to the mass parts, the modified waterborne polyurethane emulsion, carboxymethyl chitosan, modified polylactic acid, composite antibacterial agent and silane coupling agent are stirred evenly to obtain a waterproof antibacterial coating. S102. The waterproof and antibacterial coating is sprayed onto the surface of the cardboard layer, and then dried at 85°C for 60 minutes. A waterproof layer is formed through the drying and curing process, resulting in a highly waterproof and environmentally friendly packaging paper box material.

[0037] Example 3 A highly waterproof and environmentally friendly packaging paper box material includes a cardboard layer and a waterproof and antibacterial layer coated on the surface of the cardboard layer. The thickness of the waterproof and antibacterial layer is 40 micrometers. The waterproof and antibacterial layer is obtained by spraying a waterproof and antibacterial coating onto the surface of the cardboard layer and curing it. The waterproof and antibacterial coating, by mass parts, includes the following raw materials: 105g of modified waterborne polyurethane emulsion, 4g of carboxymethyl chitosan, 9g of modified polylactic acid, 1.5g of composite antibacterial agent, and 0.6g of silane coupling agent. The composite antibacterial agent is composed of modified silver-cerium-doped titanium dioxide and peppermint oil in a mass ratio of 3:2. The cardboard layer is a 300-micrometer-thick linerboard. The silane coupling agent is composed of isopropyltrioleyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane in a mass ratio of 3:4.

[0038] The above-mentioned method for preparing a highly waterproof and environmentally friendly packaging paper box material includes the following steps: S101. According to the mass parts, the modified waterborne polyurethane emulsion, carboxymethyl chitosan, modified polylactic acid, composite antibacterial agent and silane coupling agent are stirred evenly to obtain a waterproof antibacterial coating. S102. The waterproof and antibacterial coating is sprayed onto the surface of the cardboard layer, and then dried at 83°C for 65 minutes. A waterproof layer is formed through the drying and curing process, resulting in a highly waterproof and environmentally friendly packaging paper box material.

[0039] Comparative Example 1 Similar to Example 3, except that the composite antibacterial agent is modified silver-cerium-doped titanium dioxide.

[0040] Comparative Example 2 Similar to Example 3, except that the composite antibacterial agent is peppermint oil.

[0041] Comparative Example 3 Similar to Example 3, except that the silane coupling agent is isopropyltrioleoyloxytitanate.

[0042] Comparative Example 4 Same as in Example 3, except that the silane coupling agent is γ-(methacryloyloxy)propyltrimethoxysilane.

[0043] Comparative Example 5 Similar to Example 3, except that an equal amount of the aqueous polyurethane emulsion prepared in Comparative Example 1 was used instead of the modified aqueous polyurethane emulsion.

[0044] Comparative Example 6 Similar to Example 3, except that an equal amount of polylactic acid was used instead of modified polylactic acid.

[0045] Performance testing The highly waterproof and environmentally friendly packaging paperboard materials prepared in Examples 1-3 and Comparative Examples 1-6 were sampled and tested as follows. The test results are shown in Table 1.

[0046] Flame retardancy test: The sample to be tested was cut into 100×8×2mm pieces. 3 Place the sample in a glass combustion chamber, introduce a nitrogen-oxygen mixed gas flow, record the minimum oxygen concentration required for combustion, and take the average value of five tests for each group. Hydrophobicity test: Using 3 μL of deionized water as solvent, the contact angle was measured at a residence time of 3 s. The result is the average value of five different locations on the surface. The antibacterial rate was tested using the shaking method as described in GB / T20944.3-2008. Self-healing test: A scratch with a length of 400μm and a depth of 20μm was made on the surface of the protective layer, and the layer was kept in an oven at 50℃ for 12 hours. The repair rate was observed and recorded using an optical microscope. Hot water permeability test: Refer to GB / T36787-2018, place the sample to be tested on a plate lined with filter paper, pour in 100℃ hot water, let stand for 30 minutes, observe whether there is deformation, and whether there is seepage or leakage on the back. If there is no deformation, it is considered qualified. Take 10 samples from each group and record the pass rate. Hot oil permeability test: Refer to GB / T36787-2018, place the sample to be tested on a plate lined with filter paper, pour in 100℃ hot oil, let stand for 30 minutes, observe whether there is deformation and whether oil marks appear on the back, take 10 samples from each group, and record the pass rate.

[0047] Table 1 Performance Tests Analyzing the data in Table 1, we can see that: 1) The highly waterproof and environmentally friendly packaging paper box materials prepared in Examples 1-3 have excellent hydrophobic properties, antibacterial properties, flame retardancy and environmental safety, meeting the needs of the food packaging industry.

[0048] 2) The performance comparison analysis of the highly waterproof and environmentally friendly packaging paper box materials prepared in Example 3 and Comparative Examples 1-2 shows that the mass ratio of modified silver cerium doped titanium dioxide and peppermint oil is 3:2. By utilizing their synergistic effect, it can not only provide broad-spectrum and efficient antibacterial protection, but also enhance the overall antibacterial effect through their synergistic effect by utilizing their respective properties. At the same time, it brings additional functions and user experience to the packaging material.

[0049] 3) The performance comparison analysis of the high waterproof and environmentally friendly packaging paper box materials prepared in Example 3 and Comparative Examples 3-4 shows that the silane coupling agent is composed of isopropyltrioleoyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane in a mass ratio of 3:4. By utilizing their synergistic effect, the comprehensive performance of the high waterproof and environmentally friendly packaging paper box material is improved.

[0050] 4) A comparative analysis of the performance of the highly waterproof and environmentally friendly packaging paperboard materials prepared in Example 3 and Comparative Example 5 shows that the modified waterborne polyurethane emulsion successfully incorporates dihydroxybutyl polydimethylsilane into the polyurethane chain segments via fine emulsion polymerization, thus obtaining a modified waterborne polyurethane emulsion. The addition of dihydroxybutyl polydimethylsilane improves the compatibility between the polyurethane chain and the polyacrylate chain, reducing the degree of phase separation. The introduction of hydrophobic dihydroxybutyl polydimethylsilane inhibits water molecules from penetrating from the surface of the highly waterproof and environmentally friendly packaging paperboard material into the fabric interior, thereby enhancing the waterproofness of the needle-puncture resistant waterborne polyurethane coating.

[0051] 5) A comparative analysis of the performance of the highly waterproof and environmentally friendly packaging paperboard materials prepared in Example 3 and Comparative Example 6 shows that the modified polylactic acid (PLA) can effectively improve the toughness of the material by adding a modifier composed of tannic acid and phytic acid composite salt. This is because tannic acid and phytic acid composite salt can act as plasticizers, increasing the mobility between polymer chains and thus reducing the brittleness of the material. Tannic acid and phytic acid composite salt can also act as flame retardants in the material. In particular, tannic acid is a natural flame retardant that can improve the thermal stability and flame retardancy of the material. The phytic acid composite salt in the modified PLA has good water resistance, which helps to improve the overall waterproof performance of the material. The tannic acid in the modified PLA undergoes a free radical grafting reaction with sodium alginate in carboxymethyl chitosan. This chemical reaction enhances the interaction between different layers and improves the interlayer adhesion. The grafting reaction increases the complexity of the internal structure of the material, forming a more stable network structure, which not only improves the overall performance of the material but also helps to uniformly disperse the applied pressure or impact. Due to the aforementioned properties of modified polylactic acid, it can effectively extend the service life of packaging cartons, making them more suitable for the needs of the food packaging industry.

[0052] The above embodiments are only used to explain the technical solutions of this application and are not intended to limit it. Although the above embodiments have provided specific descriptions of this application, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this invention. Any modifications and equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. A highly waterproof and environmentally friendly packaging paper box, characterized in that, The invention comprises a cardboard layer and a waterproof and antibacterial layer coated on the surface of the cardboard layer. The thickness of the waterproof and antibacterial layer is 30-50 micrometers. The waterproof and antibacterial layer is prepared by spraying a waterproof and antibacterial coating onto the surface of the cardboard layer and curing it. The waterproof and antibacterial coating, by mass parts, comprises the following raw materials: 100-110 parts of modified waterborne polyurethane emulsion, 3-5 parts of carboxymethyl chitosan, 8-10 parts of modified polylactic acid, 1-2 parts of composite antibacterial agent, and 0.5-0.8 parts of silane coupling agent. The composite antibacterial agent is composed of modified silver-cerium-doped titanium dioxide and peppermint oil. The mass ratio of the modified silver-cerium-doped titanium dioxide to the peppermint oil is 3:2; The thickness of the cardboard layer is 200-400 micrometers; The preparation method of the modified waterborne polyurethane emulsion includes the following steps: S51. According to the mass fractions, 71 parts of dihydroxybutyl polydimethylsilane, 114 parts of butyl acrylate, 61 parts of styrene, 89 parts of polycaprolactone, 33 parts of isophorone diisocyanate, 3 parts of hydroxyethyl methacrylate, 1.8 parts of azobisisobutyronitrile, 0.5 parts of dibutyltin dilaurate, and 10.5 parts of n-hexadecane are mixed evenly to obtain a mixture; S52. The mixture is added to 300 parts of an emulsifier aqueous solution with a mass concentration of 6%, and then pre-emulsified at 3000 r / min to obtain a crude emulsion. Then, it is ultrasonically treated in an ice-water bath using a cell disruptor for 40 min to obtain a monomer fine emulsion. Finally, the obtained monomer fine emulsion is stirred in a nitrogen atmosphere for 1.5 h, transferred to a three-necked flask, and subjected to a fine emulsion polymerization reaction at a temperature of 72℃ in a nitrogen atmosphere for 10 h to obtain a modified waterborne polyurethane emulsion. The silane coupling agent is composed of isopropyltrioleoyloxytitanate and γ-(methacryloyloxy)propyltrimethoxysilane in a mass ratio of 3:

4.

2. The highly waterproof and environmentally friendly packaging paper box according to claim 1, characterized in that, The material of the cardboard layer is either paper bag paper or boxboard paper.

3. The highly waterproof and environmentally friendly packaging paper box according to claim 1, characterized in that, The emulsifier is 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate.

4. The highly waterproof and environmentally friendly packaging paper box according to claim 1, characterized in that, The preparation method of the modified silver-cerium-doped titanium dioxide includes the following steps: S71. At room temperature, add 100 mL of tetrabutyl titanate to a solution consisting of 160 mL of ethanol and 30 mL of deionized water, and stir for 30 min to form solution A. S72. Add 1.5g of silver nitrate and 12g of cerium nitrate to a solution consisting of 100mL of ethanol, 15mL of acetic acid and 45mL of water to form solution B; S73. Add solution B dropwise to solution A, stir for 60 min, heat to 42℃, let stand and age for 12 h, then centrifuge, wash, and dry at 80℃ for 12 h to obtain silver cerium doped titanium dioxide. S74. Mix 0.8g of γ-(methacryloyloxy)propyltrimethoxysilane with 70g of ethanol and 8g of water, and hydrolyze for 4h to obtain mixture C; S75. Add the obtained silver-cerium-doped titanium dioxide to mixture C, then heat to 43℃, stir at 300r / min for 250min, finally filter, wash, dry at 85℃ and grind to obtain modified silver-cerium-doped titanium dioxide with an average particle size of 40 nanometers.

5. The highly waterproof and environmentally friendly packaging paper box according to claim 1, characterized in that, The method for preparing the modified polylactic acid includes the following steps: S91. According to the mass fraction, 131 parts of 70% phytic acid solution, 4.6 parts of citrulline, and 0.3 parts of genipin are mixed, heated to 88℃ and kept at that temperature for 5 hours, purified with ethanol, filtered, and dried to obtain phytic acid complex salt. S92. According to the mass fraction, mix 10 parts of tannic acid and 90 parts of phytic acid composite salt, add 900 parts of polylactic acid, and mix in a high-speed mixer to obtain modified polylactic acid.

6. A method for preparing a highly waterproof and environmentally friendly packaging paper box according to any one of claims 1-5, characterized in that, Includes the following steps: S101. According to the mass parts, the modified waterborne polyurethane emulsion, carboxymethyl chitosan, modified polylactic acid, composite antibacterial agent and silane coupling agent are stirred evenly to obtain a waterproof antibacterial coating. S102. Spray the waterproof and antibacterial coating onto the surface of the cardboard layer, and then dry it at 80-85℃ for 60-70 minutes. The waterproof layer is formed through the drying and curing process, resulting in a highly waterproof and environmentally friendly packaging box.

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