Oil and water-proof catering packaging material and preparation method thereof

Abstract

The application belongs to the field of food packaging materials, and particularly relates to an oil-proof and water-proof catering packaging material and a preparation method thereof. The catering packaging material comprises a substrate layer and an oil-proof and water-proof layer, and the oil-proof and water-proof layer comprises a primer layer and a topcoat layer. The primer layer and the topcoat layer are made of degradable resins with different proportions and are respectively matched with different modified celluloses. The content of polybutylene succinate (PBS) and polybutylene adipate terephthalate (PBAT) in the primer layer is relatively high, and the content of polylactic acid (PLA) is relatively low. The primer layer is matched with acetylated cellulose, so that the primer layer has good flexibility, folding resistance and interface buffering capacity. The content of PLA in the topcoat layer is relatively high, and a proper amount of PBAT and PBS is added for toughening. The topcoat layer is matched with stearate cellulose and acetylated cellulose, so that the topcoat layer has improved surface density, hydrophobicity, oil-proof property and anti-cracking stability. Through the layering and cooperation of the primer layer and the topcoat layer, the unity of the material adhesion, folding resistance, oil-proof property, water-proof property and degradability is achieved.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials technology, and relates to an oil-proof and waterproof catering packaging material and its preparation method. Background Technology

[0002] With increasingly stringent requirements for green packaging and plastic pollution control, fiber-based materials, represented by paper, cardboard, and molded pulp products, are widely used in the food packaging industry due to their wide availability, recyclability, and biodegradability. However, paper-based and plant fiber-based materials themselves have strong hydrophilicity and porous structures, making them prone to water absorption and oil seepage. When containing water- or oil-containing foods, they are susceptible to strength reduction, leakage, and surface failure, limiting their further promotion and application in food packaging.

[0003] In existing technologies, polyethylene, polypropylene, or fluorinated oil-repellent agents are commonly used to coat the surface of paper-based materials to improve their waterproof and oil-repellent properties. While this can improve the barrier properties of paper-based materials to some extent, polyolefin coatings are difficult to degrade or recycle efficiently with the paper-based material, and fluorinated finishing systems also have issues with environmental durability and safety. Therefore, they are difficult to meet current requirements for environmentally friendly food packaging materials. In recent years, biodegradable polyester materials such as polylactic acid (PLA), polybutylene succinate (PBS), and polybutylene adipate / terephthalate (PBAT) have been increasingly used in paper-based coating systems. Among them, PLA has good rigidity and film-forming properties, while PBS and PBAT have good flexibility and processability. However, single biodegradable polyesters or simple blends still have several shortcomings, such as limited interfacial bonding with paper-based materials, insufficient melt strength, unstable surface oil and water repellency, and poor interlayer synergy, making it difficult to balance coating processability, adhesion, and final barrier properties.

[0004] Furthermore, cellulose and its derivatives possess characteristics such as renewability, biocompatibility, and biodegradability. However, natural cellulose is highly polar and has poor compatibility with hydrophobic polyester resins. When directly used in polyester systems, it easily leads to uneven dispersion, interfacial defects, and performance degradation. Modifying cellulose can improve its hydrophobicity and compatibility with the polyester matrix to a certain extent, providing a new direction for constructing paper-based coating systems that combine oil resistance, water resistance, and biodegradability. Summary of the Invention

[0005] In view of the above-mentioned defects in the prior art, the purpose of this invention is to provide an oil-proof and waterproof catering packaging material and its preparation method that improves the adhesion between the coating and the substrate, the surface density, and the oil and water resistance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An oil- and water-resistant food packaging material includes a substrate layer and an oil- and water-resistant coating, wherein the oil- and water-resistant coating includes a primer layer and a topcoat layer; by weight, wherein... The base coating comprises 85-95 parts of biodegradable resin A, 3-8 parts of acetylated cellulose, 0.5-3 parts of epoxy chain extender, 1-4 parts of plasticizer and 0-2 parts of additives; The topcoat includes 80-90 parts of biodegradable resin B, 8-15 parts of composite modified cellulose, 0.5-3 parts of epoxy chain extender, 1.5-2 parts of plasticizer, and 0-3 parts of additives; the composite modified cellulose includes stearate cellulose and acetylated cellulose, and the mass ratio of stearate cellulose to acetylated cellulose is (5-8):(2-5).

[0007] Preferably, the biodegradable resins A / B in both the primer and topcoat layers contain polybutylene succinate, polybutylene terephthalate-adipate, and polylactic acid.

[0008] Preferably, the mass ratio of polybutylene succinate, polybutylene adipate and polylactic acid in the biodegradable resin A of the base coating is (40~55):(25~35):(10~20); The mass ratio of polylactic acid, polybutylene terephthalate-adipate and polybutylene succinate in the biodegradable resin B of the topcoat is (40~50):(25~35):(8~15).

[0009] Preferably, the epoxy chain extender is one or more of the following: styrene-acrylate-glycidyl methacrylate copolymer, epoxidized styrene-acrylate copolymer, polyglycidyl methacrylate, ethylene-glycidyl methacrylate copolymer, and ethylene-acrylate-glycidyl methacrylate terpolymer. The plasticizer is one or more of the following: tributyl citrate, acetylated tributyl citrate, ethyl lactate, and oligolactic acid. The additive is one or two of an antioxidant and a lubricant in any proportion; the antioxidant is one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168 in any proportion; the lubricant is one or more of calcium stearate, zinc stearate, carnauba wax, and beeswax in any proportion.

[0010] Preferably, the acetylated cellulose in the base coating and top coating comprises cellulose, acetic anhydride and glacial acetic acid, wherein the mass ratio of cellulose, acetic anhydride and glacial acetic acid is 1:(3~4):(5~6); The stearate cellulose in the topcoat comprises cellulose and stearic anhydride, wherein the mass ratio of cellulose to stearic anhydride is 1:(2~6).

[0011] A method for preparing an oil- and water-resistant food packaging material, comprising the following steps: S1. Preparation of acetylated cellulose and stearate cellulose; S2. The biodegradable resin A is dried, and then 1 / 4 to 1 / 2 of the biodegradable resin A is melt-blended with acetylated cellulose and plasticizer. When the mixture is uniform, an epoxy chain extender is added, and the mixture is extruded and granulated to obtain a high-concentration acetylated cellulose masterbatch A. The high-concentration acetylated cellulose masterbatch A is mixed with the remaining 1 / 2 to 3 / 4 of the biodegradable resin A and then dried to obtain a base coating. S3. Dry 1 / 4 to 1 / 2 of the biodegradable resin B, then melt-blend it with stearate cellulose, acetylated cellulose and plasticizer. When the mixture is uniform, add epoxy chain extender, extrude and granulate to obtain high-concentration composite modified cellulose masterbatch B. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 1 / 2 to 3 / 4 of the biodegradable resin B uniformly, and then dry it to obtain the topcoat. S4. The base coating and top coating obtained above are cast and extruded through a co-extrusion device, coated on the surface of the substrate that has been pretreated by corona discharge, and then cooled and shaped by roll pressing. S5. Trim and roll up the molded composite material, and cure it at 35~45℃ for 24~48 hours to obtain oil-proof and waterproof catering packaging material; the substrate can be any one of paper, cardboard, or pulp molding substrate.

[0012] Preferably, the specific operation method of step S1 is as follows: S101. Dry the cellulose under vacuum at 80~100℃ and -0.03~-0.09MPa for 4~8 hours, and set aside for later use. S102. Acetic anhydride and glacial acetic acid are mixed evenly, and dried cellulose is added under heating conditions of 55~70℃. The reaction is continued for 2~4 hours. After the reaction is completed, the mixture is washed with pure water until neutral. Then, it is vacuum dried at 60~70℃ and -0.03~-0.09MPa for 3~5 hours. After pulverization, acetylated cellulose is obtained. S103. The dried cellulose is added to molten stearic anhydride at 110~130℃ and reacted under nitrogen protection for 3~5h. After the reaction is completed, the cellulose is washed with ethanol to remove impurities and then vacuum dried at 60~70℃ and -0.03~-0.09MPa for 3~5h. After pulverization, stearic acid esterified cellulose is obtained.

[0013] Preferably, the specific operation method of step S2 is as follows: S201. Polybutylene succinate, polyadipate and polylactic acid are dried and then mixed evenly in proportion to obtain biodegradable resin A. S202. Add acetylated cellulose to the above-mentioned biodegradable resin A, melt-mix at 135~170℃, mix for 5~10 min, then add plasticizer, continue stirring for 3~5 min, then add epoxy chain extender, continue stirring for 2~5 min, mix evenly, then extrude and granulate to obtain high-concentration acetylated cellulose masterbatch A. S203. Mix the high-concentration acetylated cellulose masterbatch A with the remaining 1 / 2 to 3 / 4 of the biodegradable resin A evenly, and then dry the mixture to obtain the base coating.

[0014] Preferably, the specific operation method of step S3 is as follows: S301. Polylactic acid, polyadipate and polybutylene succinate are dried and then mixed evenly in proportion to obtain biodegradable resin B. S302. Stearate cellulose and acetylated cellulose are added sequentially to the above biodegradable resin B; melt-blending is carried out at 155~175℃, and after mixing for 8~12 minutes, plasticizer is added and stirring is continued for 5~8 minutes. Then epoxy chain extender is added and stirring is continued for 2~5 minutes. After mixing evenly, the mixture is extruded and granulated to obtain high-concentration composite modified cellulose masterbatch B. S303. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 1 / 2 to 3 / 4 of the biodegradable resin B evenly, and then dry the mixture to obtain the topcoat.

[0015] Preferably, in the oil-proof and waterproof catering packaging material described in step S5, the bottom coating is in direct contact with the substrate, the top coating is located outside the bottom coating, and the thickness ratio of the bottom coating to the top coating is (1~2): (3~4).

[0016] The role and mechanism of the main components: 1. Biodegradable polyester resins: Polylactic acid mainly provides rigidity, surface hardness, film-forming properties, and coating density; polybutylene succinate mainly provides flexibility, flexural strength, stress relaxation ability, and good processing flow adaptability; polybutylene terephthalate mainly provides toughening, elongation, impact resistance, and crack propagation resistance.

[0017] 2. Acetylated cellulose and stearate cellulose 1) Acetylated cellulose improves compatibility with biodegradable polyesters, enhances film-forming continuity, reduces the hydrophilicity of natural cellulose, and strengthens the overall density of the coating. The cellulose backbone itself is relatively rigid, acting as a rigid framework and extending the penetration path within the system, thereby improving barrier stability. 2) Stearate-esterified cellulose further reduces the material's water absorption, optimizes the low polarity of the surface, improves smoothness and anti-blocking properties, and synergistically inhibits the penetration of moisture and oils along microporous channels. Because it inherently reduces polar adsorption sites, seals pores, and improves surface continuity, it achieves the goal of reducing the penetration of oils along the pores of paper fibers.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) By adjusting the ratio of polylactic acid, polybutylene succinate and polybutylene terephthalate in the base coating and the top coating, the present invention makes the base coating mainly flexible and adhesive, and the top coating mainly dense and barrier, thus realizing the functional division of the double-layer structure.

[0019] (2) The present invention introduces acetylated cellulose into the base coating, which can improve its compatibility with the biodegradable polyester system, and improve the coating continuity, cohesion and adhesion stability to the paper substrate; the introduction of stearate cellulose and acetylated cellulose into the top coating can improve the surface hydrophobicity and oil resistance while improving the dispersion uniformity, thereby improving the film density and barrier stability.

[0020] (3) By matching different resin ratios with different modified cellulose, this invention takes into account flexibility, folding resistance, adhesion, oil resistance, water resistance and processing stability, and is applicable to the field of biodegradable paper-based packaging materials. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] To achieve the above-mentioned objectives of the present invention, the technical solution of the present invention will be further described in detail below, but the scope of protection of the present invention is not limited to the following description.

[0023] An oil- and water-resistant food packaging material includes a substrate layer and an oil- and water-resistant coating, wherein the oil- and water-resistant coating includes a primer layer and a topcoat layer; by weight, wherein... (1) The base coating comprises 85-95 parts of biodegradable resin A, 3-8 parts of acetylated cellulose, 0.5-3 parts of epoxy chain extender, 1-4 parts of plasticizer, and 0-2 parts of additives; the biodegradable resin A is a compound of polybutylene succinate (PBS), polybutylene terephthalate-adipate (PBAT), and polylactic acid (PLA) in a mass ratio of (40-55): (25-35): (10-20); the acetylated cellulose is a compound of cellulose, acetic anhydride, and glacial acetic acid in a mass ratio of 1:(3-4):(5-6); The base coating contains a high proportion of PBS and PBAT, and a low proportion of PLA. PBS provides good flexibility, folding endurance, and some crystal support, while PBAT provides high ductility and crack resistance. Together, they give the base coating good stress buffering capabilities and adaptability to the rough surface structure of paper, cardboard, or pulp molding substrates during coating and subsequent molding processes. The lower proportion of PLA ensures the necessary film-forming properties and structural integrity of the underlayer, preventing excessive rigidity from weakening interfacial adhesion. The base coating is further infused with acetylated cellulose. The reduced polarity and improved compatibility of cellulose with the polyester matrix after acetylation make it easier to disperse uniformly in the PLA / PBAT / PBS system, reducing interfacial defects, improving film continuity and cohesive stability, and enhancing the adhesion stability of the base coating to the fiber substrate.

[0024] (2) The topcoat comprises 80-90 parts of biodegradable resin B, 8-15 parts of composite modified cellulose, 0.5-3 parts of epoxy chain extender, 1.5-2 parts of plasticizer, and 0-3 parts of additives; the biodegradable resin B is a compound of polylactic acid (PLA), polybutylene terephthalate (PBAT), and polybutylene succinate (PBS) in a mass ratio of (40-50):(25-35):(8-15); the composite modified cellulose is a compound of stearate cellulose and acetylated cellulose in a mass ratio of (5-8):(2-5); the stearate cellulose is a compound of cellulose and stearic anhydride in a mass ratio of 1:(2-6).

[0025] The topcoat contains a high proportion of PLA, while the proportions of PBAT and PBS are relatively low. The higher proportion of PLA is beneficial for forming a smooth, dense, and relatively hard continuous film, thus improving the material's barrier stability against moisture and oils. Adding appropriate amounts of PBAT and PBS can alleviate the inherent brittleness of the high-PLA system, reducing the risk of microcracks in the surface layer under bending, curling, stamping, and thermal changes, ensuring that the topcoat maintains a dense structure while possessing necessary flexibility and crack resistance. Stearate-modified cellulose and acetylated cellulose are further introduced into the topcoat. Stearate-modified cellulose contains long-chain hydrophobic groups, which can reduce surface polarity, decrease the tendency for water wetting and oil penetration, and improve the surface's hydrophobicity, oil resistance, and slip properties. Acetylated cellulose helps improve the dispersion and compatibility between the modified cellulose and the polyester matrix, reducing film defects caused by localized phase separation, further improving the continuity and density of the topcoat.

[0026] Both the primer and topcoat coatings mentioned above contain epoxy chain extenders, plasticizers, and additives; among them, The epoxy chain extender is one or more of the following: styrene-acrylate-glycidyl methacrylate copolymer, epoxidized styrene-acrylate copolymer, polyglycidyl methacrylate, ethylene-glycidyl methacrylate copolymer, and ethylene-acrylate-glycidyl methacrylate terpolymer. The plasticizer is one or more of the following: tributyl citrate, acetylated tributyl citrate, ethyl lactate, and oligolactic acid. The additive is one or two of an antioxidant and a lubricant in any proportion; the antioxidant is one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168 in any proportion; the lubricant is one or more of calcium stearate, zinc stearate, carnauba wax, and beeswax in any proportion.

[0027] A method for preparing an oil- and water-resistant food packaging material, comprising the following steps: S1. Preparation of acetylated cellulose and stearate cellulose, specifically: S101. Dry the cellulose under vacuum at 80~100℃ and -0.03~-0.09MPa for 4~8 hours, and set aside for later use. S102. Acetic anhydride and glacial acetic acid are mixed evenly, and dried cellulose is added under heating conditions of 55~70℃. The reaction is continued for 2~4 hours. After the reaction is completed, the mixture is washed with pure water until neutral. Then, it is vacuum dried at 60~70℃ and -0.03~-0.09MPa for 3~5 hours. After pulverization, acetylated cellulose is obtained. S103. The dried cellulose is added to molten stearic anhydride at 110~130℃ and reacted under nitrogen protection for 3~5h. After the reaction is completed, the cellulose is washed with ethanol to remove impurities and then vacuum dried at 60~70℃ and -0.03~-0.09MPa for 3~5h. After pulverization, stearic acid esterified cellulose is obtained.

[0028] S2. The biodegradable resin A is dried. Then, 1 / 4 to 1 / 2 of the biodegradable resin A is melt-blended with acetylated cellulose and a plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration acetylated cellulose masterbatch A. The high-concentration acetylated cellulose masterbatch A is then mixed uniformly with the remaining 1 / 2 to 3 / 4 of the biodegradable resin A, and dried to obtain a base coating. Specifically: S201. Polybutylene succinate, polyadipate and polylactic acid are dried and then mixed evenly in proportion to obtain biodegradable resin A. S202. Take 1 / 4 to 1 / 2 of the biodegradable resin A and melt-blend it with acetylated cellulose at 135 to 170°C. After mixing for 5 to 10 minutes, add the plasticizer and continue stirring for 3 to 5 minutes. Then add the epoxy chain extender and continue stirring for 2 to 5 minutes. After mixing evenly, extrude and granulate to obtain high-concentration acetylated cellulose masterbatch A. S203. Mix the high-concentration acetylated cellulose masterbatch A with the remaining 1 / 2 to 3 / 4 of the biodegradable resin A evenly, and then dry the mixture to obtain the base coating.

[0029] S3. 1 / 4 to 1 / 2 of the biodegradable resin B is dried, then melt-blended with stearate cellulose, acetylated cellulose, and a plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration composite modified cellulose masterbatch B. The high-concentration composite modified cellulose masterbatch B is then mixed uniformly with the remaining 1 / 2 to 3 / 4 of the biodegradable resin B, and dried to obtain a topcoat, specifically: S301. Polylactic acid, polyadipate and polybutylene succinate are dried and then mixed evenly in proportion to obtain biodegradable resin B. S302. Take 1 / 4 to 1 / 2 of the mixed resin and melt-blend it with stearic acid esterified cellulose and acetylated cellulose at 155 to 175°C. After mixing for 8 to 12 minutes, add the plasticizer and continue stirring for 5 to 8 minutes. Then add the epoxy chain extender and continue stirring for 2 to 5 minutes. After mixing evenly, extrude and granulate to obtain high-concentration composite modified cellulose masterbatch B. S303. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 1 / 2 to 3 / 4 of the biodegradable resin B evenly, and then dry the mixture to obtain the topcoat.

[0030] S4. The base coating and top coating obtained above are cast and extruded through a co-extrusion device, coated on the surface of the substrate that has been pretreated by corona discharge, and then cooled and shaped by roll pressing. S5. Trim and roll up the molded composite material, and cure it at 35~45℃ for 24~48 hours to obtain an oil-proof and waterproof catering packaging material; the substrate is any one of paper, cardboard, or pulp molding substrate; the bottom coating of the oil-proof and waterproof catering packaging material is in direct contact with the substrate, the top coating is located outside the bottom coating, and the thickness ratio of the bottom coating to the top coating is (1~2): (3~4).

[0031] Example 1 An oil- and water-resistant food packaging material includes a substrate layer and an oil- and water-resistant coating, wherein the oil- and water-resistant coating includes a primer layer and a topcoat layer; by weight, wherein... (1) The base coating comprises 90 parts of biodegradable resin A, 5 parts of acetylated cellulose, 1.5 parts of styrene-acrylate-glycidyl methacrylate copolymer, 2 parts of tributyl citrate, and 1.5 parts of additives; the biodegradable resin A is a compound of polybutylene succinate (PBS), polybutylene terephthalate-adipate (PBAT), and polylactic acid (PLA) in a mass ratio of 45:35:10; the acetylated cellulose is a compound of cellulose, acetic anhydride, and glacial acetic acid in a mass ratio of 1:4:5; the additives are a compound of antioxidant 1010 and calcium stearate, and the mass ratio of antioxidant 1010 to calcium stearate is 1:1; (2) The topcoat comprises 80 parts of biodegradable resin B, 15 parts of composite modified cellulose, 2 parts of styrene-acrylate-glycidyl methacrylate copolymer, 2 parts of tributyl citrate, and 1 part of additive (same as in step (1)); the biodegradable resin B is a compound of PLA, PBAT and PBS in a mass ratio of 45:25:10; the composite modified cellulose is a compound of stearate cellulose and acetylated cellulose in a mass ratio of 6:4; the stearate cellulose is a compound of cellulose and stearic anhydride in a mass ratio of 1:4.

[0032] A method for preparing an oil- and water-resistant food packaging material, comprising the following steps: S1. Preparation of acetylated cellulose and stearate cellulose, specifically: S101. Dry the cellulose under vacuum at 95℃ and -0.06MPa for 6 hours, and set aside for later use. S102. Acetic anhydride and glacial acetic acid were mixed evenly, and cellulose was added under heating at 65°C. The reaction was continued for 3 hours. After the reaction was completed, the mixture was washed with pure water until neutral. Then, it was vacuum dried at 65°C and -0.06 MPa for 4 hours. After pulverization, acetylated cellulose was obtained. S103. Cellulose was added to molten stearic anhydride at 120°C and reacted for 4 hours under nitrogen protection. After the reaction was completed, the mixture was washed with ethanol to remove impurities and then vacuum dried at 65°C and -0.06 MPa for 4 hours. After pulverization, stearic acid esterified cellulose was obtained.

[0033] S2. The biodegradable resin A is dried. Then, 1 / 4 of the biodegradable resin A is melt-blended with acetylated cellulose and a plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration acetylated cellulose masterbatch A. The high-concentration acetylated cellulose masterbatch A is mixed uniformly with the remaining 3 / 4 of the biodegradable resin A, and then dried to obtain a base coating, specifically: S201. Polybutylene succinate, polyadipate and polylactic acid are dried and then mixed evenly in proportion to obtain biodegradable resin A. S202. Take 1 / 4 of the biodegradable resin A and melt-blend it with acetylated cellulose at 155°C. After mixing for 8 minutes, add the plasticizer and continue stirring for 4 minutes. Then add the epoxy chain extender and continue stirring for 3 minutes. After mixing evenly, extrude and granulate to obtain high-concentration acetylated cellulose masterbatch A. S203. Mix the high-concentration acetylated cellulose masterbatch A with the remaining 3 / 4 of the biodegradable resin A evenly, and then dry the mixture to obtain the base coating.

[0034] S3. 1 / 4 of the biodegradable resin B is dried, then melt-blended with stearate cellulose, acetylated cellulose, and a plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration composite modified cellulose masterbatch B. The high-concentration composite modified cellulose masterbatch B is mixed uniformly with the remaining 3 / 4 of the biodegradable resin B, and then dried to obtain a topcoat, specifically: S301. Polylactic acid, polyadipate and polybutylene succinate are dried and then mixed evenly in proportion to obtain biodegradable resin B. S302. Take 1 / 4 of the biodegradable resin B, first melt-blend it with stearate cellulose and acetylated cellulose at 165℃, mix for 10 min, then add plasticizer, continue stirring for 6 min, then add epoxy chain extender, continue stirring for 4 min, mix evenly, then extrude and granulate to obtain high-concentration composite modified cellulose masterbatch B. S303. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 3 / 4 of the biodegradable resin B evenly, and then dry the mixture to obtain the topcoat.

[0035] S4. The base coating and top coating obtained above are cast and extruded through a co-extrusion device, coated on the surface of the corona-pretreated paperboard, and then cooled and shaped by roll pressing. S5. Trim and roll up the molded composite material, and cure it at 40°C for 36 hours to obtain an oil-proof and waterproof catering packaging material. In the oil-proof and waterproof catering packaging material, the bottom coating is in direct contact with the substrate, and the top coating is located outside the bottom coating. The thickness ratio of the bottom coating to the top coating is 2:3.

[0036] Example 2 An oil- and water-resistant food packaging material includes a substrate layer and an oil- and water-resistant coating, wherein the oil- and water-resistant coating includes a primer layer and a topcoat layer; by weight, wherein... (1) The base coating comprises 95 parts of biodegradable resin A, 3 parts of acetylated cellulose, 0.5 parts of epoxidized styrene-acrylate copolymer, 1 part of acetylated tributyl citrate, and 0.5 parts of additives; the biodegradable resin A is a compound of polybutylene succinate (PBS), polybutylene terephthalate-adipate (PBAT), and polylactic acid (PLA) in a mass ratio of 55:25:15; the acetylated cellulose is a compound of cellulose, acetic anhydride, and glacial acetic acid in a mass ratio of 1:3:6; the additives include antioxidant 1076 and zinc stearate, and the mass ratio of antioxidant 1076 to zinc stearate is 1:2; (2) The topcoat comprises 85 parts of biodegradable resin B, 10 parts of composite modified cellulose, 1.5 parts of epoxidized styrene-acrylate copolymer, 1.5 parts of acetylated tributyl citrate, and 2 parts of additives (same as in step (1)); the biodegradable resin B is a compound of PLA, PBAT and PBS in a mass ratio of 40:30:15; the composite modified cellulose is a compound of stearate cellulose and acetylated cellulose in a mass ratio of 5:5; the stearate cellulose is a compound of cellulose and stearic anhydride in a mass ratio of 1:6.

[0037] A method for preparing an oil- and water-resistant food packaging material, comprising the following steps: S1. Preparation of acetylated cellulose and stearate cellulose, specifically: S101. Dry the cellulose under vacuum at 100℃ and -0.03MPa for 4 hours, and set aside for later use. S102. Acetic anhydride and glacial acetic acid are mixed evenly, and cellulose is added under heating at 70°C. The reaction is continued for 2 hours. After the reaction is completed, the mixture is washed with pure water until neutral. Then, it is vacuum dried at 70°C and -0.03 MPa for 3 hours. After pulverization, acetylated cellulose is obtained. S103. Cellulose was added to molten stearic anhydride at 130°C and reacted for 3 hours under nitrogen protection. After the reaction was completed, the mixture was washed with ethanol to remove impurities and then dried under vacuum at 60°C and -0.03 MPa for 5 hours. After pulverization, stearic acid esterified cellulose was obtained.

[0038] S2. The biodegradable resin A is dried. Then, half of the biodegradable resin A is melt-blended with acetylated cellulose and a plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration acetylated cellulose masterbatch A. The high-concentration acetylated cellulose masterbatch A is mixed uniformly with the remaining half of the biodegradable resin A, and then dried to obtain a base coating, specifically: S201. Polybutylene succinate, polyadipate and polylactic acid are dried and then mixed evenly in proportion to obtain biodegradable resin A. S202. Take 1 / 2 of the biodegradable resin A and melt-blend it with acetylated cellulose at 170°C. After mixing for 5 minutes, add the plasticizer and continue stirring for 3 minutes. Then add the epoxy chain extender and continue stirring for 2 minutes. After mixing evenly, extrude and granulate to obtain high-concentration acetylated cellulose masterbatch A. S203. Mix the high-concentration acetylated cellulose masterbatch A with the remaining 1 / 2 of the biodegradable resin A evenly, and then dry the mixture to obtain the base coating.

[0039] S3. Half of the biodegradable resin B is dried, then melt-blended with stearate cellulose, acetylated cellulose, and plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration composite modified cellulose masterbatch B. The high-concentration composite modified cellulose masterbatch B is mixed uniformly with the remaining half of the biodegradable resin B, and then dried to obtain a topcoat, specifically: S301. Polylactic acid, polyadipate and polybutylene succinate are dried and then mixed evenly in proportion to obtain biodegradable resin B. S302. Take 1 / 2 of the biodegradable resin B and first mix it with stearic acid esterified cellulose and acetylated cellulose. Melt-mix it at 175°C for 12 minutes, then add the plasticizer and continue stirring for 8 minutes. After that, add the epoxy chain extender and continue stirring for 2 minutes. After mixing evenly, extrude and granulate to obtain high-concentration composite modified cellulose masterbatch B. S303. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 1 / 2 of the biodegradable resin B evenly, and then dry the mixture to obtain the topcoat.

[0040] S4. The base coating and top coating obtained above are cast and extruded through a co-extrusion device, coated on the surface of paper that has been pretreated by corona discharge, and then cooled and shaped by roll pressing. S5. Trim and roll up the molded composite material, and cure it at 45°C for 24 hours to obtain an oil-proof and waterproof catering packaging material; the bottom coating of the oil-proof and waterproof catering packaging material is in direct contact with the substrate, the top coating is located outside the bottom coating, and the thickness ratio of the bottom coating to the top coating is 1:4.

[0041] Example 3 An oil- and water-resistant food packaging material includes a substrate layer and an oil- and water-resistant coating, wherein the oil- and water-resistant coating includes a primer layer and a topcoat layer; by weight, wherein... (1) The base coating comprises 85 parts of biodegradable resin A, 8 parts of acetylated cellulose, 3 parts of polyglycidyl methacrylate, and 4 parts of ethyl lactate; the biodegradable resin A is a compound of polybutylene succinate (PBS), polybutylene terephthalate-adipate (PBAT), and polylactic acid (PLA) in a mass ratio of 40:25:20; the acetylated cellulose is a compound of cellulose, acetic anhydride, and glacial acetic acid in a mass ratio of 1:4:5; (2) The topcoat comprises 90 parts of biodegradable resin B, 8 parts of composite modified cellulose, 0.5 parts of polyglycidyl methacrylate, and 1.5 parts of ethyl lactate; the biodegradable resin B is a compound of PLA, PBAT and PBS in a mass ratio of 50:32:8; the composite modified cellulose is a compound of stearate cellulose and acetylated cellulose in a mass ratio of 8:2; the stearate cellulose is a compound of cellulose and stearic anhydride in a mass ratio of 1:2.

[0042] A method for preparing an oil- and water-resistant food packaging material, comprising the following steps: S1. Preparation of acetylated cellulose and stearate cellulose, specifically: S101. Dry the cellulose under vacuum at 80℃ and -0.09MPa for 8 hours, and set aside for later use. S102. Acetic anhydride and glacial acetic acid were mixed evenly, and cellulose was added under heating at 55°C and the reaction was continued for 4 hours. After the reaction was completed, the mixture was washed with pure water until neutral, and then vacuum dried at 60°C and -0.09 MPa for 5 hours. After pulverization, acetylated cellulose was obtained. S103. Cellulose was added to molten stearic anhydride at 110°C and reacted for 5 hours under nitrogen protection. After the reaction was completed, the mixture was washed with ethanol to remove impurities and then vacuum dried at 70°C and -0.09 MPa for 3 hours. After pulverization, stearic acid esterified cellulose was obtained.

[0043] S2. The biodegradable resin A is dried. Then, 1 / 4 of the biodegradable resin A is melt-blended with acetylated cellulose and a plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration acetylated cellulose masterbatch A. The high-concentration acetylated cellulose masterbatch A is mixed uniformly with the remaining 3 / 4 of the biodegradable resin A, and then dried to obtain a base coating, specifically: S201. Polybutylene succinate, polyadipate and polylactic acid are dried and then mixed evenly in proportion to obtain biodegradable resin A. S202. Take 1 / 4 of the biodegradable resin A and melt-blend it with acetylated cellulose at 135°C. After mixing for 10 minutes, add the plasticizer and continue stirring for 5 minutes. Then add the epoxy chain extender and continue stirring for 5 minutes. After mixing evenly, extrude and granulate to obtain high-concentration acetylated cellulose masterbatch A. S203. Mix the high-concentration acetylated cellulose masterbatch A with the remaining 3 / 4 of the biodegradable resin A evenly, and then dry the mixture to obtain the base coating.

[0044] S3. Half of the biodegradable resin B is dried, then melt-blended with stearate cellulose, acetylated cellulose, and plasticizer. Finally, an epoxy chain extender is added, and after uniform mixing, it is extruded and granulated to obtain a high-concentration composite modified cellulose masterbatch B. The high-concentration composite modified cellulose masterbatch B is mixed uniformly with the remaining half of the biodegradable resin B, and then dried to obtain a topcoat, specifically: S301. Polylactic acid, polyadipate and polybutylene succinate are dried and then mixed evenly in proportion to obtain biodegradable resin B. S302. Take 1 / 2 of the biodegradable resin B, first melt-blend it with stearate cellulose and acetylated cellulose at 155℃, mix for 8 minutes, then add plasticizer, continue stirring for 5 minutes, then add epoxy chain extender, continue stirring for 5 minutes, mix evenly, then extrude and granulate to obtain high-concentration composite modified cellulose masterbatch B. S303. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 1 / 2 of the biodegradable resin B evenly, and then dry the mixture to obtain the topcoat.

[0045] S4. The base coating and top coating obtained above are cast and extruded through a co-extrusion device, coated on the molded surface of the pulp that has been pretreated by corona discharge, and then cooled and shaped by roll pressing. S5. Trim and roll up the molded composite material, and cure it at 45°C for 24 hours to obtain an oil-proof and waterproof catering packaging material; the bottom coating of the oil-proof and waterproof catering packaging material is in direct contact with the substrate, the top coating is located outside the bottom coating, and the thickness ratio of the bottom coating to the top coating is 1:4.

[0046] Comparative Example 1 Compared with Example 1, the cellulose in the base coating and top coating is not esterified, and the other operations and parameters are completely the same as in Example 1.

[0047] Comparative Example 2 Compared with Example 1, both the base coating and the top coating use a single biodegradable resin, and the remaining operations and parameters are completely consistent with Example 1.

[0048] Comparative Example 3 Compared with Example 1, the acetylated cellulose and composite modified cellulose described in the base coating and top coating improve the degree of cellulose esterification by doubling the amount of esterification reagent (the mass ratio of cellulose, acetic anhydride and glacial acetic acid in acetylated cellulose is 1:8:5; the mass ratio of cellulose and stearic anhydride in stearic acid esterified cellulose is 1:8); the remaining operations and parameters are completely consistent with Example 1.

[0049] Comparative Example 4 Compared with Example 1, the oil-proof and waterproof layer only uses a top coating, and the rest of the operation and parameters are completely the same as in Example 1.

[0050] The performance of the food packaging materials prepared in Examples 1-3 and Comparative Examples 1-4 was tested, and the results are shown in Table 1. The performance testing methods are as follows: (1) Water contact angle: The contact angle meter was used for testing. About 5 μL of deionized water was dropped onto the material surface, and the static contact angle of the droplet on the sample surface was recorded. The test was repeated 3 times in parallel, and the average value was taken.

[0051] (2) Water absorption rate: The material was treated and weighed under constant temperature and drying conditions. Then the material was immersed in deionized water for 30 minutes. After taking it out, the surface moisture was absorbed with filter paper and weighed again to calculate the water absorption rate. Each group was tested in parallel 3 times and the average value was taken.

[0052] (3) Oil resistance: The Kit oil resistance rating method is used for determination. Different grades of standard test solutions are dropped onto the sample surface in sequence. After standing for a specified time, observe whether the sample surface penetrates, darkens, or the back side is oil-permeable. The highest grade that does not penetrate is taken as the oil resistance rating.

[0053] (4) Tensile strength & elongation at break: Both were tested using a universal testing machine. The maximum stress the material was subjected to before fracture and the elongation at fracture were recorded. The tensile strength was recorded and the elongation at break was calculated.

[0054] (5) Degradability: The material was cut and weighed, and placed in a simulated composting environment or soil degradation environment for degradation treatment. The material was taken out on the 30th and 90th days, respectively. The surface attachments were cleaned, dried to constant weight, and then weighed to calculate its retention rate.

[0055] As shown in Table 1, the oil-proof and waterproof catering packaging material prepared in the embodiments of the present invention is superior to the comparative example in terms of water contact angle, water absorption rate, oil resistance, tensile strength and elongation at break. This indicates that the use of PBS, PBAT and PLA compound resin, combined with acetylated cellulose and stearate cellulose to construct a double-layer structure of base coating / top coating can significantly improve the oil-proof and waterproof performance and mechanical properties of the material.

[0056] In contrast, in Comparative Example 1, the cellulose was not esterified, resulting in poor compatibility with the biodegradable resin matrix. The water contact angle was only 87.5°, the water absorption rate increased to 11.6%, the oil repellency grade decreased to level 5, and the tensile strength and elongation at break were significantly reduced, indicating that unmodified cellulose is not conducive to system dispersion and interfacial bonding. In Comparative Example 2, both the base coating and top coating used a single biodegradable resin, lacking the synergistic effect between PBS, PBAT, and PLA, resulting in poor overall material performance, especially with an elongation at break of only 76%, indicating significantly insufficient toughness. Simultaneously, the 90-day weight retention rate was 40.8%, indicating that its degradation balance was also unsatisfactory. Comparative Example 3… Increasing the degree of esterification of cellulose improved the hydrophobicity and oil resistance of the material surface, with a water contact angle of 121.5° and an oil resistance rating of 12. However, the tensile strength and elongation at break decreased, and the weight retention rates at 30 days and 90 days reached 92.8% and 49.7%, respectively. This indicates that although excessive esterification can improve short-term barrier performance, it weakens the material's toughness and significantly reduces the degradation rate. In Comparative Example 4, only a top coating was used without a base coating, resulting in a lack of flexible buffer and adhesion transition layer between the material and the substrate. Although its surface barrier performance was acceptable, the water absorption rate, tensile strength, and elongation at break were all lower than those of Example 1, indicating that the double-layer structure design is beneficial for improving overall performance.

[0057] Therefore, this invention, through the dual-layer synergistic design of the base coating and top coating, and the matching of acetylated cellulose / composite modified cellulose with PBS, PBAT, and PLA compound system, can effectively improve the surface hydrophobicity, oil barrier properties, mechanical strength, and toughness of oil-proof and waterproof catering packaging materials, while maintaining good biodegradability, and has good application prospects.

[0058] Finally, it should be noted that although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. An oil- and water-resistant food packaging material, characterized in that, It includes a substrate layer and an oil- and water-resistant coating, wherein the oil- and water-resistant coating includes a primer and a topcoat; by weight, wherein, The base coating comprises 85-95 parts of biodegradable resin A, 3-8 parts of acetylated cellulose, 0.5-3 parts of epoxy chain extender, 1-4 parts of plasticizer and 0.5-2 parts of additives; The topcoat includes 80-90 parts of biodegradable resin B, 8-15 parts of composite modified cellulose, 0.5-3 parts of epoxy chain extender, and 1.5-2 parts of plasticizer; the composite modified cellulose includes stearate cellulose and acetylated cellulose, and the mass ratio of stearate cellulose to acetylated cellulose is (5-8):(2-5).

2. The oil-proof and waterproof catering packaging material according to claim 1, characterized in that, The biodegradable resin A and biodegradable resin B described in the primer and topcoat both contain polybutylene succinate, polybutylene terephthalate-adipate, and polylactic acid.

3. The oil-proof and waterproof catering packaging material according to claim 2, characterized in that, The mass ratio of polybutylene succinate, polybutylene adipate and polylactic acid in the biodegradable resin A of the base coating is (40~55):(25~35):(10~20); The mass ratio of polylactic acid, polybutylene terephthalate-adipate and polybutylene succinate in the biodegradable resin B of the topcoat is (40~50):(25~35):(8~15).

4. The oil-proof and waterproof catering packaging material according to claim 1, characterized in that, The epoxy chain extender is one or more of the following: styrene-acrylate-glycidyl methacrylate copolymer, epoxidized styrene-acrylate copolymer, polyglycidyl methacrylate, ethylene-glycidyl methacrylate copolymer, and ethylene-acrylate-glycidyl methacrylate terpolymer. The plasticizer is one or more of the following: tributyl citrate, acetylated tributyl citrate, ethyl lactate, and oligolactic acid. The additive is one or two of an antioxidant and a lubricant in any proportion; the antioxidant is one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168 in any proportion; the lubricant is one or more of calcium stearate, zinc stearate, carnauba wax, and beeswax in any proportion.

5. The oil-proof and waterproof catering packaging material according to any one of claims 2 to 4, characterized in that, The acetylated cellulose in the base coating and top coating comprises cellulose, acetic anhydride and glacial acetic acid, wherein the mass ratio of cellulose, acetic anhydride and glacial acetic acid is 1:(3~4):(5~6); The stearate cellulose in the topcoat comprises cellulose and stearic anhydride, wherein the mass ratio of cellulose to stearic anhydride is 1:(2~6).

6. A method for preparing an oil- and water-resistant catering packaging material, used to prepare the oil- and water-resistant catering packaging material according to claim 5, characterized in that, Includes the following steps: S1. Preparation of acetylated cellulose and stearate cellulose; S2. The biodegradable resin A is dried, and then 1 / 4 to 1 / 2 of the biodegradable resin A is melt-blended with acetylated cellulose and plasticizer. When the mixture is uniform, an epoxy chain extender is added, and the mixture is extruded and granulated to obtain a high-concentration acetylated cellulose masterbatch A. The high-concentration acetylated cellulose masterbatch A is mixed with the remaining 1 / 2 to 3 / 4 of the biodegradable resin A and then dried to obtain a base coating. S3. Dry 1 / 4 to 1 / 2 of the biodegradable resin B, then melt-blend it with stearate cellulose, acetylated cellulose and plasticizer. When the mixture is uniform, add epoxy chain extender, extrude and granulate to obtain high-concentration composite modified cellulose masterbatch B. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 1 / 2 to 3 / 4 of the biodegradable resin B uniformly, and then dry it to obtain the topcoat. S4. The base coating and top coating obtained above are cast and extruded through a co-extrusion device and coated on the surface of the substrate layer that has been pretreated by corona discharge, and then cooled and shaped by roll pressing; the substrate can be any one of paper, paperboard, or pulp molding substrate; S5. Trim and roll up the molded composite material, and cure it at 35~45℃ for 24~48 hours to obtain oil-proof and waterproof catering packaging material.

7. The method for preparing the oil- and water-resistant catering packaging material according to claim 6, characterized in that, The specific operation method of step S1 is as follows: S101. Dry the cellulose under vacuum at 80~100℃ and -0.03~-0.09MPa for 4~8 hours, and set aside for later use. S102. Acetic anhydride and glacial acetic acid are mixed evenly, and dried cellulose is added under heating conditions of 55~70℃. The reaction is continued for 2~4 hours. After the reaction is completed, the mixture is washed with pure water until neutral. Then, it is vacuum dried at 60~70℃ and -0.03~-0.09MPa for 3~5 hours. After pulverization, acetylated cellulose is obtained. S103. The dried cellulose is added to molten stearic anhydride at 110~130℃ and reacted under nitrogen protection for 3~5h. After the reaction is completed, the cellulose is washed with ethanol to remove impurities and then vacuum dried at 60~70℃ and -0.03~-0.09MPa for 3~5h. After pulverization, stearic acid esterified cellulose is obtained.

8. The method for preparing the oil-proof and waterproof catering packaging material according to claim 6 or 7, characterized in that, The specific operation method of step S2 is as follows: S201. Polybutylene succinate, polyadipate and polylactic acid are dried and then mixed evenly in proportion to obtain biodegradable resin A. S202. Add acetylated cellulose to the above-mentioned biodegradable resin A, melt-mix at 135~170℃, mix for 5~10 min, then add plasticizer, continue stirring for 3~5 min, then add epoxy chain extender, continue stirring for 2~5 min, mix evenly, then extrude and granulate to obtain high-concentration acetylated cellulose masterbatch A. S203. Mix the high-concentration acetylated cellulose masterbatch A with the remaining 1 / 2 to 3 / 4 of the biodegradable resin A evenly, and then dry the mixture to obtain the base coating.

9. The method for preparing the oil-proof and waterproof catering packaging material according to claim 8, characterized in that, The specific operation method of step S3 is as follows: S301. Polylactic acid, polyadipate and polybutylene succinate are dried and then mixed evenly in proportion to obtain biodegradable resin B. S302. Stearate cellulose and acetylated cellulose are added sequentially to the above biodegradable resin B; melt-blending is carried out at 155~175℃, and after mixing for 8~12 minutes, plasticizer is added and stirring is continued for 5~8 minutes. Then epoxy chain extender is added and stirring is continued for 2~5 minutes. After mixing evenly, the mixture is extruded and granulated to obtain high-concentration composite modified cellulose masterbatch B. S303. Mix the high-concentration composite modified cellulose masterbatch B with the remaining 1 / 2 to 3 / 4 of the biodegradable resin B evenly, and then dry the mixture to obtain the topcoat.

10. The method for preparing the oil-proof and waterproof catering packaging material according to claim 9, characterized in that, In step S5, the base coating of the oil-proof and waterproof catering packaging material is in direct contact with the substrate, and the top coating is located outside the base coating. The thickness ratio of the base coating to the top coating is (1~2): (3~4).

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