A packaging coating material and a packaging coating

Abstract

The present application relates to the technical field of environment-friendly packaging materials, and particularly relates to a packaging coating material, a packaging coating and a preparation method thereof, according to weight parts, the packaging coating material comprises the following components: 20-50 parts of ethylene-acrylic acid copolymer; 30-60 parts of polyhydroxyalkanoate; 5-25 parts of modified lignin; and 0.5-3 parts of processing aid; the modified lignin is at least one of acetylated lignin, hydroxypropylated lignin and carboxylated lignin. The packaging coating material provided by the present application is fully biobased and degradable, and a small amount of ethylene-acrylic acid copolymer is used, so that the overall coating can be completely degraded in industrial composting, the prepared coating has the effects of waterproofing, oil-proofing, oxygen and moisture resistance and ultraviolet shielding, and has a balance between rigidity and toughness.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly packaging materials technology, and in particular to a packaging coating material and a packaging coating. Background Technology

[0002] With the increasing prominence of microplastic pollution caused by traditional petroleum-based non-degradable packaging coatings (such as PE lamination and polypropylene coatings), the development of fully biodegradable, high-performance packaging coatings has become a research hotspot in the industry. Among them, coatings on paper-based or other biodegradable substrates mainly serve to block moisture and oxygen, as well as provide heat sealing functions.

[0003] Polyhydroxyalkanoates (PHAs) are a class of fully biodegradable bio-based polymers with good biocompatibility and industrial compostability, making them an ideal substrate to replace traditional petroleum-based packaging materials. However, single PHA coatings suffer from drawbacks such as poor adhesion, weak low-temperature heat-sealing performance, brittle mechanical properties, and mediocre oxygen and moisture barrier properties, limiting their large-scale application in the packaging field. Therefore, how to balance the biodegradability, mechanical properties, and barrier properties of packaging coatings is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] To address the problem that existing packaging coatings struggle to simultaneously achieve biodegradability, mechanical properties, and barrier properties, this invention provides a packaging coating material. This material, through the synergistic effect of ethylene-acrylic acid copolymers, modified lignin, and polyhydroxyalkanoates (PHA), achieves simultaneous improvement in biodegradability, mechanical properties, and barrier properties, thus solving the problem of existing packaging coatings failing to achieve these three objectives.

[0005] The technical solution adopted by this invention to solve its technical problem is: A packaging coating material, comprising the following components by weight: 20-50 parts of ethylene-acrylic acid copolymer; 30-60 parts of polyhydroxyalkanoates; 5-25 parts of modified lignin; Processing aids: 0.5-3 parts; The modified lignin is selected from at least one of acetylated lignin, hydroxypropylated lignin, and carboxylated lignin.

[0006] Optionally, the ethylene-acrylic acid copolymer is selected from at least one of ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer.

[0007] Optionally, the mass content of acrylic acid monomer in the ethylene-acrylic acid copolymer is 6%-20%, and the melt flow rate is not less than 6g / 10min (190℃, 2.16kg).

[0008] Optionally, the melt flow rate of the polyhydroxyalkanoate is 3~15 g / 10 min (190 °C, 2.16 kg).

[0009] Optionally, the polyhydroxyalkanoate is selected from at least one of PHB, PHBV, and P3HB4HB.

[0010] Optionally, the processing aid is selected from at least one of lubricants, antioxidants, and chain extenders.

[0011] Optionally, the lubricant is selected from at least one of stearic acid and zinc stearate.

[0012] Optionally, the antioxidant is selected from at least one of antioxidant 1010 and antioxidant 168.

[0013] Optionally, the chain extender is selected from at least one of isocyanate chain extenders and epoxy chain extenders.

[0014] Another object of the present invention is to provide a packaging coating prepared by means of packaging coating materials as described above.

[0015] The beneficial effects of this invention are: The packaging coating material provided by this invention uses PHA and modified lignin as fully bio-based biodegradable components, combined with a small amount of ethylene-acrylic acid copolymer. The overall coating can be completely degraded by industrial composting, leaving no microplastic residue and meeting environmental packaging requirements. The ethylene-acrylic acid copolymer effectively improves the problems of poor melt strength and film formation difficulty of PHA, enabling low-temperature heat sealing and adapting to existing industrial coating production lines without equipment modification. The prepared coating has significant waterproof, oil-proof, oxygen and moisture barrier, and UV shielding effects, with a balanced mechanical rigidity and toughness, resistance to rubbing and bending, and strong adhesion to paper, aluminum foil, and bio-based films without delamination. The raw materials contain no toxic additives, meet the safety standards for food contact materials, and are suitable for various food packaging. By using lignin to replace part of the bio-based polymer, the cost of raw materials is reduced, achieving high-value utilization of agricultural and forestry by-products. Detailed Implementation

[0016] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0017] To address the problem that existing packaging coatings struggle to simultaneously achieve biodegradability, mechanical properties, and barrier properties, this invention provides a packaging coating material, comprising the following components by weight: 20-50 parts of ethylene-acrylic acid copolymer; Polyhydroxyalkanoate (PHA) 30-60 parts; 5-25 parts of modified lignin; Processing aids: 0.5-3 parts; The modified lignin is selected from at least one of acetylated lignin, hydroxypropylated lignin, and carboxylated lignin.

[0018] Lignin, a byproduct of agricultural and forestry biomass, is widely available and inexpensive. It possesses excellent properties such as UV shielding, anti-oxidation, oxygen and moisture barrier, and enhanced rigidity. Furthermore, it is completely biodegradable, making it an ideal bio-based functional filler. However, direct use of lignin is problematic because of its poor compatibility with polymers and tendency to agglomerate, making it impossible to directly blend and prepare coatings with uniform performance. Therefore, this invention employs modified lignin to improve its compatibility with polymer matrices. As a functional reinforcing phase, it provides UV shielding, oxygen and moisture barrier, and anti-oxidation properties, thereby enhancing the rigidity and thermal stability of the coating and reducing overall raw material costs.

[0019] Specifically, acetylated lignin can significantly improve its compatibility with polymers; lignin itself is rich in hydrophilic hydroxyl groups, which makes it easy to aggregate in non-polar polymer matrices; while the acetylation reaction reduces the polarity of lignin by introducing hydrophobic acetyl groups, making it closer to the surface energy of polymers, thereby reducing the tendency of phase separation.

[0020] The present invention preferably uses acetylated lignin as an acetylated lignin / montmorillonite composite modified material, and further preferably uses the acetylated lignin / montmorillonite composite modified material prepared according to the following method: S1: Dispersed preparation Add alkali lignin to an ethanol-water mixture (ethanol:water volume ratio = 1:2), stir and disperse for 30-60 minutes to obtain a uniform alkali lignin suspension.

[0021] S2: Preprocessing Stir continuously at room temperature to allow the alkali lignin to fully swell and disperse evenly in the mixed solvent.

[0022] S3: Adsorption Load Montmorillonite was added to the system at a mass ratio of alkali lignin to montmorillonite of 1:8, and the mixture was stirred continuously at room temperature until adsorption reached equilibrium.

[0023] S4: Solid-liquid separation After the adsorption equilibrium is reached, the mixed system is centrifuged or filtered to separate the solid composite filter cake.

[0024] S5: Drying process The solid filter cake was dried to remove solvent and moisture, resulting in an acetylated lignin / montmorillonite composite modified material.

[0025] Hydroxypropylated lignin can effectively block the phenolic hydroxyl groups in lignin that have low reactivity and are prone to causing material embrittlement by grafting flexible propyl chains with reactive hydroxyl groups onto lignin. At the same time, it can introduce aliphatic hydroxyl groups with higher reactivity and more flexible structure, so that the modified lignin can be better dispersed in the polymer.

[0026] The present invention preferably uses hydroxypropylated lignin as a hydroxypropylated lignin / montmorillonite composite material, and further preferably uses this hydroxypropylated lignin / montmorillonite composite material prepared by the following method: S1: Dispersed preparation Alkali lignin was added to an ethanol-water mixed solution (ethanol:water volume ratio = 1:2), and stirred and dispersed for 30-60 minutes to prepare a uniform lignin suspension.

[0027] S2: Alkaline activation Sodium hydroxide was added to the suspension to adjust the pH of the system to 11-13, and the mixture was stirred at room temperature for 30 min to activate the phenolic hydroxyl active sites of lignin.

[0028] S3: Modification reaction Under nitrogen protection, propylene oxide was added dropwise to the system, and the molar ratio of alkali lignin to propylene oxide was controlled at 1:1.2 to 3.0. The temperature was raised to 50 to 70 °C, and the reaction was stirred at a constant temperature for 2 to 5 h to complete the hydroxypropylation modification of lignin.

[0029] S4: Adsorption Loading The reaction system was cooled to room temperature, and montmorillonite was added at a mass ratio of alkali lignin to montmorillonite of 1:8. The mixture was stirred at room temperature for 4–8 h until adsorption equilibrium was reached.

[0030] S5: Separation and Drying The solid product was separated by centrifugation / vacuum filtration, washed with deionized water until neutral, dried under vacuum at 60-80 °C for 12-24 h, pulverized and sieved to obtain hydroxypropylated lignin / montmorillonite composite material.

[0031] The carboxyl groups introduced by carboxylated lignin can form a dense hydrogen bond network with polar groups in the polymer matrix. This strong physical interaction can effectively anchor lignin, prevent its aggregation, and significantly enhance interfacial bonding.

[0032] The present invention preferably uses carboxylated lignin as a carboxylated lignin / montmorillonite composite material, and further preferably uses a carboxylated lignin / montmorillonite composite material prepared according to the following method: S1: Dispersed preparation Alkali lignin was added to an ethanol-water mixed solution (ethanol:water volume ratio = 1:2) and stirred for 30-60 minutes to obtain a uniform lignin suspension.

[0033] S2: Alkaline activation Add sodium hydroxide to adjust the pH of the system to 10-12, stir at room temperature for 30 min to activate the lignin reaction sites.

[0034] S3: Modification reaction Sodium chloroacetate was added to the system, and the molar ratio of alkali lignin to sodium chloroacetate was controlled at 1:1.0 to 2.5. The temperature was raised to 60 to 80 °C and the reaction was carried out at a constant temperature for 3 to 6 h to complete the lignin carboxymethylation (carboxylation) modification.

[0035] S4: Adsorption Loading The reaction solution was cooled to room temperature, and montmorillonite was added at a mass ratio of alkali lignin to montmorillonite of 1:8. The mixture was stirred at room temperature for 4–8 hours until adsorption reached equilibrium.

[0036] S5: Separation and Drying The solid product was collected by centrifugation or vacuum filtration, washed with water until neutral, dried under vacuum at 60-80 °C for 12-24 h, pulverized and sieved to obtain carboxylated lignin / montmorillonite composite material.

[0037] Ethylene-acrylic acid copolymers possess excellent adhesion, low-temperature heat-sealing properties, and water and oil resistance. They exhibit strong adhesion to various packaging substrates and can effectively improve the film-forming properties and processability of polymer coatings. This invention further preferably selects at least one of ethylene-acrylic acid copolymers (EAA) and ethylene-methacrylic acid copolymers (EMAA). Through in-situ compatibilization modification with EAA / EMAA, the modified lignin is uniformly dispersed in the polymer matrix, resulting in a coating that possesses excellent water and oil resistance, low-temperature heat-sealing properties, high barrier properties, UV shielding, and a balance of mechanical rigidity and toughness. Furthermore, it can achieve complete industrial composting degradation without microplastic residue, making it suitable for food packaging substrates such as paper-based, aluminum foil, and bio-based films.

[0038] The packaging coating material provided by this invention uses PHA and modified lignin as fully bio-based biodegradable components, combined with a small amount of EAA / EMAA. The overall coating can achieve complete industrial composting degradation with no microplastic residue, meeting environmental packaging requirements. EAA / EMAA effectively improves the problems of poor melt strength and film formation difficulty of PHA, enabling low-temperature heat sealing and adapting to existing industrial coating production lines without equipment modification. The prepared coating has significant waterproof, oil-proof, oxygen and moisture barrier, and UV shielding effects, with a balanced mechanical rigidity and toughness, resistance to rubbing and bending, and strong adhesion to paper, aluminum foil, and bio-based films without delamination. The raw materials contain no toxic additives, meet food contact material safety standards, and are suitable for various food packaging. By using lignin to replace part of the bio-based polymer, the cost of raw materials is reduced, achieving high-value utilization of agricultural and forestry by-products.

[0039] This invention solves the technical problems of poor adhesion, weak heat-sealing properties, brittle mechanical properties, and insufficient barrier properties of single PHA coatings, as well as the poor biodegradability and poor lignin compatibility of EAA / EMAA, through the synergistic effect of ethylene-acrylic acid copolymer (EAA / EMAA), modified lignin, and polyhydroxyalkanoate (PHA). It prepares a packaging coating that is biodegradable, has high adhesion, high barrier properties, heat-sealing properties, and UV resistance.

[0040] The ethylene-acrylic acid copolymer (EAA / EMAA) in this invention serves as both the binder and the continuous phase, providing excellent substrate adhesion, low-temperature heat-sealing properties, and water and oil resistance. Simultaneously, it in-situ compatibilizes PHA and lignin, improving system compatibility and film-forming properties. Preferably, the ethylene-acrylic acid copolymer contains 6%-20% acrylic acid monomer by mass, with a melt flow rate of not less than 6 g / 10 min (190°C, 2.16 kg). Further, this invention preferably contains 9%-15% acrylic acid monomer by mass, with a melt flow rate of 8-20 g / 10 min (190°C, 2.16 kg), ensuring the final coating's adhesion strength to the substrate and the melt flow, coating smoothness, density, and coating efficiency during extrusion coating.

[0041] Furthermore, the present invention preferably uses at least one of the Dow / SK Primacor series and the ExxonMobil Escor / Exxtra Adhere series as the ethylene-methacrylic acid copolymer (EAA) and at least one of the DuPont / Dow Nucrel series to adapt to their melt coating processes.

[0042] The polyhydroxyalkanoate in this invention serves as a degradable matrix phase, providing the coating with fully biodegradable and industrial compostable properties, and endowing the coating with basic toughness and bio-based properties. Specifically, the melt flow rate of the polyhydroxyalkanoate is preferably 3~15g / 10min (190℃, 2.16kg), and more preferably the polyhydroxyalkanoate is selected from at least one of PHB, PHBV, and P3HB4HB to adapt to the melt coating process.

[0043] In this invention, the processing aid is used to improve the processing fluidity of the system, prevent high-temperature degradation, and enhance the crosslinking density and mechanical properties of the coating. Preferably, the processing aid is selected from at least one of lubricant, antioxidant, and chain extender. More preferably, the lubricant is selected from at least one of stearic acid and zinc stearate. Preferably, the antioxidant is selected from at least one of antioxidant 1010 and antioxidant 168. Preferably, the chain extender is selected from at least one of isocyanate chain extender and epoxy chain extender.

[0044] The packaging coating material provided by this invention has a simple preparation process, can be adapted to existing melt extrusion and coating industrial production lines, has low raw material costs, meets food contact packaging safety standards, and has broad market application prospects.

[0045] Another object of the present invention is to provide a packaging coating prepared by means of packaging coating materials as described above.

[0046] The packaging coating provided by this invention uses PHA and modified lignin in its raw materials as fully bio-based biodegradable components. Combined with a small amount of EAA / EMAA, the overall coating can achieve complete industrial composting degradation with no microplastic residue, meeting environmental packaging requirements. EA / EMAA effectively improves the problems of poor melt strength and film formation difficulty of PHA, enabling low-temperature heat sealing and compatibility with existing industrial coating production lines without equipment modification. The prepared coating exhibits significant waterproof, oil-proof, oxygen and moisture barrier, and UV shielding effects. It also possesses a balanced mechanical rigidity and toughness, is resistant to rubbing and bending, and exhibits strong adhesion to paper, aluminum foil, and bio-based films without delamination. The raw materials contain no toxic additives, meet food contact material safety standards, and are suitable for various food packaging applications. By using lignin to replace part of the bio-based polymer, raw material costs are reduced, achieving high-value utilization of agricultural and forestry by-products.

[0047] The packaging coating of this invention can be prepared using any existing method. For example, the packaging coating can be prepared according to the following method: S1: According to the formula, mix the ethylene-acrylic acid copolymer (EAA / EMAA), polyhydroxyalkanoate, modified lignin, and processing aids to obtain a premix; In this preferred step, EAA / EMAA, PHA, modified lignin, and processing aids are weighed according to the formula and put into a high-speed mixer. They are mixed at room temperature for 10-20 minutes to obtain a uniform premix. S2: Add the premixed material to a twin-screw extruder, and after melt blending and extrusion granulation, obtain coating-specific masterbatch; Preferably, the temperature range of the twin-screw extruder in this step is 160-185℃, and the screw speed is 150-300 r / min; S3: Apply the coating masterbatch to the surface of the substrate using melt coating or roller coating equipment, and obtain the packaging coating after drying and curing; Preferably, in this step, the coating masterbatch is applied to the surface of a paper-based, aluminum foil, or bio-based film substrate using melt coating or roller coating equipment, and after drying and curing, a ternary blend biodegradable packaging coating is obtained; the coating temperature is 170-190℃, the curing temperature is 90-110℃, and the curing time is 1-2 minutes.

[0048] The preferred coating amount of this invention is 5~12g / m², Cobb60 water absorption rate ≤20g / m², oil resistance Kit value ≥5, oxygen permeability ≤50cm³ / (m²·24h·0.1MPa), and ultraviolet blocking rate ≥90%.

[0049] Alternatively, the packaging coating can be prepared as follows: S1: According to the formula, add polyhydroxy fatty acid ester, modified lignin and processing aid into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premixed material to a twin-screw extruder, melt extrude and granulate the material at 170°C, and the screw speed is 200 r / min to obtain a coating-specific composite masterbatch; S3: In an alkaline solution at 96-99℃, the ethylene-acrylic acid copolymer is dissolved into an aqueous dispersion of the ethylene-acrylic acid copolymer with a solid content of 15-25%. S4: The coating-specific composite masterbatch obtained in S2 is coarsely crushed to 20–80 mesh, and then premixed with 160–250 parts of an ethylene-acrylic acid copolymer aqueous dispersion with a solid content of 15%–25% by high-speed stirring. S5: Place the wetted premixed material in a closed low temperature environment of -25℃~-15℃ for freeze ultrafine grinding for 30–120 min, control the particle size D90≤5 μm, and obtain a uniform and stable bio-based composite water-based material. S6: Allow the mixture to slowly return to room temperature naturally, then add appropriate amounts of deionized water, defoamer, wetting and leveling agent, film-forming aid, and thickener; adjust the viscosity and pH to stabilize the system, then stir and homogenize in stages at high and low speeds, and finally filter to obtain the finished water-based coating. S7: Apply the finished water-based coating to the surface of the paper cup / board, cure at 130℃ for 30 seconds, coating amount 8-10g / m². 2 This yields the packaging coating.

[0050] The substrate in this invention can be one of food packaging paper, paper cup paperboard, aluminum foil composite substrate, or PLA film. The EAA / EMAA-lignin-PHA ternary blend biodegradable packaging coating provided by this invention can be applied to the food packaging field, specifically for waterproofing, oil-proofing, freshness-preserving, and heat-sealing packaging of oily foods, baked goods, fresh foods, and dried foods.

[0051] The packaging coating preparation method provided by this invention is simple. The PHA and modified lignin in the raw materials are fully bio-based and biodegradable components. With the addition of a small amount of EAA / EMAA, the overall coating can achieve complete degradation through industrial composting, leaving no microplastic residues and meeting environmental packaging requirements. EAA / EMAA effectively improves the problems of poor melt strength and film formation difficulty of PHA, enabling low-temperature heat sealing. It is compatible with existing industrial coating production lines without the need for equipment modification. The prepared coating has significant waterproof, oil-proof, oxygen and moisture barrier, and UV shielding effects. It has a balanced mechanical rigidity and toughness, is resistant to rubbing and bending, and has strong adhesion to paper, aluminum foil, and bio-based films without delamination. The raw materials contain no toxic additives, meet the safety standards for food contact materials, and are suitable for various food packaging. By using lignin to replace part of the bio-based polymer, the cost of raw materials is reduced, and the high-value utilization of agricultural and forestry by-products is achieved.

[0052] This invention provides a ternary blend biodegradable packaging coating of EAA / EMAA-lignin-PHA, which achieves a balance of biodegradability, processability, and functionality through the scientific ratio and synergistic effect of the three components.

[0053] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0054] Unless otherwise specified, the ethylene-acrylic acid copolymer (EAA) in the embodiments and comparative examples of this invention is from the Dow / SK Primacor series, and the ethylene-methacrylic acid copolymer (EMAA) is from the DuPont / Dow Nucrel series.

[0055] The acrylic monomer content is 12% by mass, and the melt flow rate is 14 g / 10 min (190℃, 2.16 kg).

[0056] Unless otherwise specified, the melt flow rate of the polyhydroxyalkanoates in the embodiments and comparative examples of the present invention is 9 g / 10 min (190 °C, 2.16 kg).

[0057] Unless otherwise specified, the acetylated lignin in the embodiments and comparative examples of the present invention is prepared according to the following method: S1 Dispersed Formulation Alkali lignin was added to an ethanol-water mixture (ethanol:water volume ratio = 1:2) and stirred for 45 minutes to obtain a uniform alkali lignin suspension.

[0058] S2 Preprocessing Stir continuously at room temperature to allow the alkali lignin to fully swell and disperse evenly in the mixed solvent.

[0059] S3 Adsorption Loading Montmorillonite was added to the system at a mass ratio of alkali lignin to montmorillonite of 1:8, and the mixture was stirred continuously at room temperature until adsorption reached equilibrium.

[0060] S4 Solid-Liquid Separation After the adsorption equilibrium is reached, the mixed system is centrifuged or filtered to separate the solid composite filter cake.

[0061] S5 Drying Treatment The solid filter cake was dried to remove solvent and moisture, resulting in an acetylated lignin / montmorillonite composite modified material.

[0062] Unless otherwise specified, the hydroxypropylated lignin in the embodiments and comparative examples of the present invention is prepared according to the following method: S1 Dispersed Formulation Alkali lignin was added to an ethanol-water mixed solution (ethanol:water volume ratio = 1:2), stirred and dispersed for 45 min to prepare a uniform lignin suspension.

[0063] S2 alkaline activation Sodium hydroxide was added to the suspension to adjust the pH of the system to 12, and the mixture was stirred at room temperature for 30 min to activate the phenolic hydroxyl active sites of lignin.

[0064] S3 Modification Reaction Under nitrogen protection, propylene oxide was added dropwise to the system, and the molar ratio of alkali lignin to propylene oxide was controlled at 1:2.1. The temperature was raised to 60 °C, and the reaction was stirred at a constant temperature for 4 h to complete the hydroxypropylation modification of lignin.

[0065] S4 Adsorption Loading The reaction system was cooled to room temperature, and montmorillonite was added at a mass ratio of alkali lignin to montmorillonite of 1:8. The mixture was stirred at room temperature for 6 hours until adsorption equilibrium was reached.

[0066] S5 Separation and Drying The solid product was separated by centrifugation / filtration, washed with deionized water until neutral, vacuum dried at 70 °C for 18 h, pulverized and sieved to obtain hydroxypropylated lignin / montmorillonite composite material.

[0067] Unless otherwise specified, the carboxylated lignin in the embodiments and comparative examples of the present invention is prepared according to the following method: S1 Dispersed Formulation Alkali lignin was added to an ethanol-water mixture (ethanol:water volume ratio = 1:2) and stirred for 45 min to obtain a uniform lignin suspension.

[0068] S2 alkaline activation Add sodium hydroxide to adjust the pH of the system to 11, stir at room temperature for 30 min to activate the lignin reaction sites.

[0069] S3 Modification Reaction Sodium chloroacetate was added to the system, and the molar ratio of alkali lignin to sodium chloroacetate was controlled at 1:1.8. The temperature was raised to 70℃ and the reaction was carried out at a constant temperature for 4.5 h to complete the lignin carboxymethylation (carboxylation) modification.

[0070] S4 Adsorption Loading The reaction solution was cooled to room temperature, and montmorillonite was added at a mass ratio of alkali lignin to montmorillonite of 1:8. The mixture was stirred at room temperature for 6 hours until adsorption reached equilibrium.

[0071] S5 Separation and Drying The solid product was collected by centrifugation or vacuum filtration, washed with water until neutral, dried under vacuum at 70 °C for 18 h, pulverized and sieved to obtain carboxylated lignin / montmorillonite composite material.

[0072] Example 1

[0073] This embodiment provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 30 parts of EAA, 45 parts of PHBV, 12 parts of acetylated lignin / montmorillonite composite modifier, 0.8 parts of zinc stearate, and 0.5 parts of antioxidant 1010. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of food packaging paper at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, and obtain a coating amount of 8g / m².

[0074] Example 2

[0075] This embodiment provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 40 parts of EAA, 40 parts of P3HB4HB, 15 parts of hydroxypropylated lignin / montmorillonite composite material, 1.0 part of stearic acid, and 0.6 parts of epoxy chain extender. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of the aluminum foil substrate at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, with a coating amount of 10g / m², to obtain the packaging coating.

[0076] Example 3

[0077] This embodiment provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 25 parts EAA, 50 parts PHB, 8 parts carboxylated lignin / montmorillonite composite material, 0.7 parts zinc stearate, and 0.4 parts antioxidant 168. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: The coating masterbatch is coated onto the surface of the PLA bio-based film at 180°C using a melt coating equipment, cured at 105°C for 1.5 min, with a coating amount of 6 g / m², to obtain the packaging coating.

[0078] Example 4

[0079] This embodiment provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 30 parts EMAA, 50 parts PHB, 8 parts carboxylated lignin / montmorillonite composite material, 0.7 parts zinc stearate, and 0.4 parts antioxidant 168. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: The coating masterbatch is coated onto the surface of the PLA bio-based film at 180°C using a melt coating equipment, cured at 105°C for 1.5 min, with a coating amount of 6 g / m², to obtain the packaging coating.

[0080] Example 5

[0081] This embodiment provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 35 parts of EAA, 50 parts of PHBV / P3HB4HB mixed PHA (mass ratio 1:1), 15 parts of acetylated lignin / montmorillonite composite modifier, 0.9 parts of stearic acid, and 0.5 parts of isocyanate chain extender. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of paper cups and paperboards at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, and obtain a coating amount of 9g / m² to achieve the packaging coating.

[0082] Example 6

[0083] This embodiment provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 30 parts EAA, 20 parts EMAA, 32 parts PHBV / P3HB4HB mixed PHA (mass ratio 1:1), 18 parts acetylated lignin / montmorillonite composite modifier, 0.9 parts stearic acid, and 0.5 parts isocyanate chain extender. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of paper cups and paperboards at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, and obtain a coating amount of 9g / m² to achieve the packaging coating.

[0084] Example 7

[0085] This embodiment provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 42 parts of PHBV / P3HB4HB mixed PHA (mass ratio 1:1), 18 parts of acetylated lignin / montmorillonite composite modifier, 0.9 parts of stearic acid, and 0.5 parts of isocyanate chain extender. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premixed material to a twin-screw extruder, melt extrude and granulate the material at 170°C, and the screw speed is 200 r / min to obtain a coating-specific composite masterbatch; S3: Dissolve EAA in an alkaline solution at 96-99℃ to form an EAA aqueous dispersion with a solid content of 20%; S4: The coating-specific composite masterbatch obtained in S2 is coarsely crushed to 20–80 mesh, and then premixed with 200 parts of EAA aqueous dispersion with a solid content of 20% by high-speed stirring and wetting. S5: Place the wetted premixed material in a -20℃ closed low temperature environment for freeze ultrafine grinding for 80 min, control the particle size D90≤5 μm, and obtain a uniform and stable bio-based composite water-based material. S6: Allow the mixture to slowly return to room temperature naturally, then add appropriate amounts of deionized water, defoamer, wetting and leveling agent, film-forming aid, and thickener; adjust the viscosity and pH to stabilize the system, then stir and homogenize in stages at high and low speeds, and finally filter to obtain the finished water-based coating. S7: Apply the finished water-based coating to the surface of the paper cup / board, cure at 130℃ for 30 seconds, with a coating amount of 9g / m², to obtain the packaging coating.

[0086] Each comparative example in this invention is compared with Example 1.

[0087] Comparative Example 1 This comparative example provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh 45 parts of PHBV according to the weight ratio and add them to a twin-screw extruder. Melt extrusion granulation is performed in the twin-screw extruder at 170℃ with a screw speed of 200r / min to obtain coating masterbatch. S2: The coating masterbatch is applied to the surface of food packaging paper at 180°C using a melt coating equipment, cured at 105°C for 1.5 minutes, with a coating amount of 8g / m², to obtain the packaging coating.

[0088] Comparative Example 2 This comparative example provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 30 parts EAA, 45 parts PHBV, 0.8 parts zinc stearate, and 0.5 parts antioxidant 1010. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of food packaging paper at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, and obtain a coating amount of 8g / m².

[0089] Comparative Example 3 This comparative example provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 45 parts of PHBV, 12 parts of acetylated lignin / montmorillonite composite modifier, 0.8 parts of zinc stearate, and 0.5 parts of antioxidant 1010. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of food packaging paper at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, and obtain a coating amount of 8g / m².

[0090] Comparative Example 4 This comparative example provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 30 parts of EAA, 12 parts of acetylated lignin / montmorillonite composite modifier, 0.8 parts of zinc stearate, and 0.5 parts of antioxidant 1010. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of food packaging paper at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, and obtain a coating amount of 8g / m².

[0091] Comparative Example 5 This comparative example provides a method for preparing a packaging coating, which includes the following steps: S1: Weigh out the following by weight: 40 parts EAA, 40 parts P3HB4HB, 15 parts lignin, 1.0 part stearic acid, and 0.6 parts epoxy chain extender. Put them into a high-speed mixer and mix at room temperature for 15 minutes to obtain a uniform premix. S2: Add the premix to a twin-screw extruder, melt extrude and granulate the twin-screw extruder at 170°C, and the screw speed is 200 r / min to obtain coating masterbatch; S3: Apply the coating masterbatch to the surface of the aluminum foil substrate at 180°C using a melt coating equipment, cure at 105°C for 1.5 minutes, with a coating amount of 10g / m², to obtain the packaging coating.

[0092] The performance of the packaging coatings prepared in the above embodiments and comparative examples was tested using the following methods: Cobb 60 water absorption rate: Tested according to ISO 535:2023 "Determination of water absorption of paper and paperboard - Cobb method" for 60 seconds. Oil resistance kit value: Refer to TAPPI T 559 cm_22 standard; Oxygen permeability: tested according to ASTM F1927_20 under 23℃ and 50% RH conditions; tested according to ASTM D3985_24 under dry conditions; Ultraviolet blocking rate: Refer to GB / T 23983-2009 "Determination of ultraviolet transmittance and yellowness index of plastic films and sheets"; Heat seal strength: Refer to ASTM F88 / F88M_23 "Standard Test Method for Heat Seal Strength of Flexible Barrier Materials"; 90-day degradation rate of industrial compost: Refer to GB / T 19277.1-2011 "Determination of final aerobic biodegradation capacity of materials under controlled composting conditions"; Substrate adhesion: Rating from 0 to 5 according to ISO 2409:2020 "Coatings and varnishes - cross-cut adhesion test". Coating rigidity: The number of double folds is tested according to ISO 5626:1993 "Determination of folding endurance of paper" to reflect the coating rigidity.

[0093] The test results are shown in Table 1.

[0094] Table 1 Example 1 16g / m² Level 6 38 93% 8.2 92% Level 0 Flexural endurance > 90 cycles Example 2 12g / m² Level 7 29 96% 9.5 90% Level 0 Flexural endurance > 100 cycles Example 3 18g / m² Level 5 45 91% 7.6 94% Level 0 Flexural endurance > 85 times Example 4 15g / m² Level 6 32 95% 8.8 91% Level 0 Flexural endurance > 90 cycles Example 5 12g / m² Level 6 32 95% 9.0 95% Level 0 Flexural endurance > 90 cycles Example 6 10g / m² Level 6 40 95% 10.0 85% Level 0 Flexural endurance > 100 cycles Example 7 14g / m² Level 7 30 95% 9.0 93% Level 0 Flexural endurance > 100 cycles Comparative Example 1 42g / m² Level 3 120 20% 3.1 90% Level 2 Flexural endurance <30 times Comparative Example 2 28g / m² Level 4 75 35% 5.3 70% Level 1 50 folding resistance Comparative Example 3 35g / m2 Level 4 90 85% 2.4 88% Level 3 Flexural endurance <20 times Comparative Example 4 20g / m2 Level 5 60 35% 7.0 35% Level 0 120 folding resistance Comparative Example 5 50g / m2 Level 0 Beyond measurement range 80% 4.5 85% Level 2 Flexural endurance <20 times As can be seen from the data in the table above, the EAA / EMAA-lignin-PHA ternary blend biodegradable packaging coating prepared in the various embodiments of the present invention can be widely used in paper cups, lunch boxes, food packaging bags, aluminum-plastic composite packaging, fresh food preservation packaging, baked goods packaging and other fields. It can completely replace traditional PE coating and non-degradable petroleum-based coating. The process is mature, can be continuously and scaled up, complies with the national plastic restriction and environmental protection policies and food contact material safety standards, and has extremely strong industrial transformation value.

[0095] Comparative Example 1 is a single PHA coating, which has insufficient barrier properties, weak heat sealing properties, brittle mechanical properties, poor coating adhesion, and is prone to delamination and cracking.

[0096] The difference between Comparative Example 2 and Example 1 is that no modified lignin was added, resulting in insufficient barrier properties of the coating, as well as insufficient rigidity and easy deformation of the coating.

[0097] The difference between Comparative Example 3 and Example 1 is that EAA was not added, the substrate adhesion was grade 3, the coating peeled off over a large area, the heat seal strength was 2.4 N / 15 mm, and the film-forming properties were poor and the film was brittle.

[0098] The difference between Comparative Example 4 and Example 1 is that PHA was not added. The industrial compost had a degradation rate of only 35% after 90 days, which could not be completely degraded and did not meet the requirements for biodegradable packaging.

[0099] The difference between Comparative Example 5 and Example 1 is that unmodified lignin was used instead of modified lignin. Due to the poor compatibility between unmodified lignin and the matrix, the coating agglomerated and delaminated, resulting in a decrease in barrier performance. The UV blocking rate was only 80%, the substrate adhesion was grade 2, and the heat sealing strength was 4.5 N / 15 mm.

[0100] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A packaging coating material, characterized in that, Based on parts by weight, it includes the following components: 20-50 parts of ethylene-acrylic acid copolymer; 30-60 parts of polyhydroxyalkanoates; Modified lignin, 5-25 parts; Processing aids: 0.5-3 parts; The modified lignin is selected from at least one of acetylated lignin, hydroxypropylated lignin, and carboxylated lignin.

2. The packaging coating material as described in claim 1, characterized in that, The ethylene-acrylic acid copolymer is selected from at least one of ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer.

3. The packaging coating material as described in claim 1, characterized in that, The ethylene-acrylic acid copolymer contains 6%-20% acrylic acid monomer by mass, and the melt flow rate is not less than 6g / 10min (190℃, 2.16kg).

4. The packaging coating material as described in claim 1, characterized in that, The melt flow rate of the polyhydroxy fatty acid ester is 3~15 g / 10 min (190℃, 2.16 kg).

5. The packaging coating material as described in claim 4, characterized in that, The polyhydroxy fatty acid ester is selected from at least one of PHB, PHBV, and P3HB4HB.

6. The packaging coating material as described in claim 1, characterized in that, The processing aid is selected from at least one of lubricants, antioxidants, and chain extenders.

7. The packaging coating material as described in claim 6, characterized in that, The lubricant is selected from at least one of stearic acid and zinc stearate.

8. The packaging coating material as described in claim 6, characterized in that, The antioxidant is selected from at least one of antioxidant 1010 and antioxidant 168.

9. The packaging coating material as described in claim 6, characterized in that, The chain extender is selected from at least one of isocyanate chain extenders and epoxy chain extenders.

10. A packaging coating, characterized in that, It is prepared by means of the packaging coating material as described in any one of claims 1-9.