Preparation method of environment-friendly PLA coating high-temperature-resistant and grease-resistant hot-drink cup

Abstract

This invention discloses a method for preparing an environmentally friendly PLA-coated high-temperature and grease-resistant hot beverage cup, relating to the field of polyester biodegradable plastics technology. The specific steps of the method are: substrate pretreatment, bridging agent coating, composite coating preparation, in-situ polymerization reaction, and post-molding treatment. This invention uses a bio-based coupling bridging agent to react with the active groups on the substrate surface to form a chemically bonded layer, replacing the traditional physical adhesion method and eliminating coating peeling problems, while providing a stable substrate for composite coating polymerization. A temperature-sensitive composite coating is constructed by in-situ polymerization of PLA and PLGA, adapting to different usage scenarios and blocking the penetration of grease and heat. The entire system uses biodegradable components, ensuring simultaneous natural degradation after disposal, fully preserving the environmental protection attributes throughout the entire life cycle, and effectively solving the core pain points of traditional biodegradable hot beverage cups, such as unstable structure and insufficient practical performance.

Description

Technical Field

[0001] This invention relates to the field of polyester biodegradable plastics technology, specifically to a method for preparing an environmentally friendly PLA-coated high-temperature and grease-resistant hot beverage cup. Background Technology

[0002] Hot beverage cups are commonly used containers in catering services and daily consumption, and are widely used for holding and carrying hot drinks such as coffee, milk tea, and hot soup. Their convenience and practicality have made them an indispensable part of modern life. With the awakening of global environmental awareness and the gradual tightening of environmental policies, traditional hot beverage cups that rely on non-degradable plastic coatings can no longer meet the needs of green development because they are difficult to degrade naturally and easily cause environmental pollution. The application of biodegradable materials in the field of hot beverage cups has become an inevitable trend in the industry.

[0003] Existing biodegradable hot beverage cups mostly use PLA as the coating material, but there are some defects at the core technology level. They lack an effective interface bonding mechanism, and the coating and the substrate, as well as the layers of the coating, are only physically attached, making them prone to peeling during use. The coating does not have temperature-sensitive response characteristics, making it difficult to form a stable barrier structure in hot beverage scenarios, and its resistance to oil penetration and high temperature is insufficient. The degradation characteristics of the coating and the substrate are mismatched, resulting in damage to the environmental friendliness throughout the entire life cycle. At the same time, the interface treatment and polymerization stages in the existing preparation process are not designed reasonably, failing to form a coherent technical system, which affects the stability of product use and application effect. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing an environmentally friendly PLA-coated high-temperature and grease-resistant hot beverage cup. This invention uses a bio-based coupling bridging agent to react with the active groups on the substrate surface to form a chemically bonded layer, replacing the traditional physical adhesion method and eliminating coating peeling problems. At the same time, it provides a stable substrate for the polymerization of the composite coating. A temperature-sensitive composite coating is constructed by in-situ polymerization of PLA and PLGA, which is suitable for different usage scenarios and blocks the penetration of grease and heat. The entire system uses biodegradable components to ensure simultaneous natural degradation after disposal, fully retaining the environmental protection attributes throughout the entire life cycle, effectively solving the core pain points of traditional biodegradable hot beverage cups, such as unstable structure and insufficient practical performance.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing an environmentally friendly PLA-coated high-temperature and grease-resistant hot beverage cup, the specific steps of which are as follows:

[0006] Substrate pretreatment: Select biodegradable paper substrate or PLA substrate, and preheat it after cleaning and drying;

[0007] Bridging agent coating: The bio-based coupling bridging agent is dissolved in anhydrous ethanol to prepare a bridging agent solution, which is then coated on the surface of the pretreated biodegradable paper substrate or PLA substrate, and a chemical bonding layer is formed after heat preservation.

[0008] Preparation of composite coating solution: Weigh PLA and PLGA, add organic solvent and stir to dissolve to form composite coating solution;

[0009] In-situ polymerization reaction: The composite coating liquid is applied to the surface of the biodegradable paper substrate or PLA substrate after being coated with the bridging agent solution, and then placed in a reaction vessel and nitrogen gas is introduced to carry out the in-situ polymerization reaction to form a temperature-sensitive composite coating.

[0010] Post-molding treatment: The biodegradable paper substrate or PLA substrate with the temperature-sensitive composite coating is cooled to room temperature, cut, molded and then vacuum dried to obtain an environmentally friendly PLA-coated high-temperature and oil-resistant hot beverage cup.

[0011] Furthermore, in the substrate pretreatment, the biodegradable paper substrate is cleaned with deionized water, and the PLA substrate is wiped with anhydrous ethanol; after cleaning, the biodegradable paper substrate or PLA substrate is dried in a vacuum drying oven, and the preheating temperature of the dried biodegradable paper substrate or PLA substrate is 100-120℃, and the preheating time is 30-60min.

[0012] Furthermore, in the substrate pretreatment, the biodegradable paper substrate is dried in a vacuum drying oven at a temperature of 60-70℃ for 1.5-2 hours; the PLA substrate is dried in a vacuum drying oven at a temperature of 50-60℃ for 1-1.5 hours.

[0013] Furthermore, in the bridging agent coating, the bio-based coupling bridging agent is one or a combination of two of polylactic acid diisocyanate and lignin-based coupling agent. When the combination is made up, the mass ratio of polylactic acid diisocyanate to lignin-based coupling agent is 1:1-3:1. When the compounded bio-based coupling bridging agent is dissolved, the stirring rate is 300-500 r / min, the stirring time is 15-30 min, and the mass concentration of the bridging agent solution is 5-15%.

[0014] Furthermore, in the bridging agent coating process, the bridging agent solution is applied by spraying or roller coating, and the coating amount is 5-20 g / m². 2 When selecting roller coating, the roller speed is 20-30 r / min and the coating pressure is 0.1-0.3 MPa; when selecting spray coating, the spraying pressure is 0.2-0.4 MPa and the nozzle distance is 15-25 cm from the surface of the pretreated biodegradable paper substrate or PLA substrate.

[0015] Furthermore, in the bridging agent coating process, the heat preservation process is carried out in a constant temperature oven with an air velocity of 0.5-1 m / s, a heat preservation temperature of 80-100℃, and a heat preservation time of 20-40 min. After the heat preservation is completed, the material is allowed to cool naturally to room temperature for 20-30 min. The chemical bonding layer is a thin film formed by the reaction of a bio-based coupling bridging agent with surface active groups of a biodegradable paper substrate or PLA substrate, with a thickness of 1-3 μm.

[0016] Furthermore, in the preparation of the composite coating solution, the mass ratio of PLA to PLGA is 7:3-9:1, the number average molecular weight of PLA is 50,000-100,000, the molar ratio of lactic acid to glycolic acid of PLGA is 7:3-8:2, and the number average molecular weight is 40,000-80,000; the organic solvent is a mixed solvent of dichloromethane and N,N-dimethylformamide at a volume ratio of 3:1, or a mixed solvent of dichloromethane and acetone at a volume ratio of 4:1, and the total mass ratio of the organic solvent to PLA+PLGA is 3.6:1-9:1; PLA is first added to the organic solvent and dissolved for 30-40 minutes, then PLGA is added and the mixture is stirred and dissolved. The stirring environment temperature is 25-35℃, and the stirring time is 60-90 minutes.

[0017] Furthermore, in the in-situ polymerization reaction, the coating amount of the composite coating solution is 20-50 g / m³. 2 The coating method is either spraying or roller coating. When roller coating is selected, the roller speed is 25-35 r / min and the coating pressure is 0.2-0.4 MPa. When spraying is selected, the spraying pressure is 0.3-0.5 MPa and the nozzle distance from the surface of the biodegradable paper substrate or PLA substrate is 20-30 cm.

[0018] Furthermore, in the in-situ polymerization reaction, the temperature inside the reactor is 110-140℃, the polymerization pressure is 0.3-0.8MPa, and the reaction time is 60-120min; the nitrogen gas introduction rate is 1-3L / min, the reactor heating rate is 2-5℃ / min, and the cooling rate after the reaction is completed is 3-5℃ / min; the temperature-sensitive composite coating is a composite layer formed by the in-situ polymerization reaction of PLA and PLGA, with a thickness of 5-10μm.

[0019] Furthermore, in the post-molding treatment, the molding temperature is 80-100℃, the molding pressure is 1-2MPa, and the holding time is 10-20min; the vacuum drying temperature is 60-80℃, the drying time is 12-24h, and the vacuum degree is -0.08 to -0.1MPa; during the drying process, ventilation is carried out once every 6 hours, and each ventilation lasts for 15-20min.

[0020] Compared with existing technologies, this method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup has the following advantages:

[0021] I. This invention introduces a bio-based coupling bridging agent between the substrate and the subsequent composite coating, allowing the bridging agent to react with the active groups on the substrate surface to form a stable chemical bond layer. This creates a strong connection interface between the substrate and the coating, replacing the traditional physical adhesion method and fundamentally preventing coating peeling during use. This chemical bond layer not only enhances the bonding stability between the substrate and the composite coating but also provides a good reaction substrate for the in-situ polymerization of the subsequent PLA / PLGA composite coating, ensuring the integrity and continuity of the coating structure and guaranteeing the structural stability of the hot beverage cup under different usage scenarios.

[0022] II. This invention constructs a temperature-sensitive composite coating through the in-situ polymerization reaction of PLA and PLGA. Utilizing the temperature-sensitive properties of PLGA itself, the composite coating forms a dense barrier structure in the hot beverage container environment, preventing the penetration of oils and heat. At room temperature, it maintains a flexible state to adapt to usage requirements. At the same time, both PLA and PLGA are biodegradable polyester materials, which, together with the bio-based coupling bridging agent and biodegradable substrate, constitute a fully biodegradable system. This ensures that the hot beverage cup can achieve synchronous natural degradation after disposal, fully retaining its environmental protection attributes throughout its entire life cycle. This not only solves the problem of insufficient practical performance of traditional biodegradable hot beverage cups, but also adheres to the core environmental protection requirements.

[0023] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0025] Figure 1 A flowchart illustrating the preparation method of an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup;

[0026] Figure 2 A framework diagram of a method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup;

[0027] Figure 3This diagram illustrates the steps of the in-situ polymerization reaction in the preparation of an environmentally friendly, high-temperature, and grease-resistant PLA-coated hot beverage cup. Detailed Implementation

[0028] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0029] Example 1:

[0030] For the use of biodegradable paper-based hot beverage cups in chain coffee shops, these cups are suitable for everyday serving of freshly ground coffee, lattes, and other beverages at 80-90℃. They need to meet the requirements of high-frequency stacking and storage, rapid dispensing, and long-term heat preservation without leakage. The specific preparation process for this biodegradable paper substrate is as follows: A 220g / m³ weight of... 2 The high-stiffness biodegradable paper substrate can withstand stacking more than 20 pieces in a coffee shop without deformation. High-pressure deionized water spraying is used to clean the surface of residual pulp fibers and production dust. Immediately after cleaning, it is placed in a vacuum drying oven and dried at 68℃ for 1.9 hours to ensure the moisture content of the biodegradable paper substrate meets the requirements for subsequent coating. Then, the dried biodegradable paper substrate is neatly laid out on a multi-layer material rack and placed in a constant-temperature oven for preheating. The oven temperature is set to 115℃ and preheated for 40 minutes to thoroughly remove trace amounts of bound water inside the substrate and activate the surface hydroxyl groups, preparing for the subsequent bridging reaction. Figure 1 As shown.

[0031] A bio-based coupling bridging agent, a mixture of polylactic acid diisocyanate and lignin-based coupling agent at a mass ratio of 2:1, was selected. This mixture balances adhesion and environmental friendliness. After being dissolved in anhydrous ethanol, the mixture was stirred at 450 rpm for 25 minutes to prepare a 12% (w / w) bridging agent solution. The solution was then uniformly coated onto the pretreated biodegradable paper substrate using a roller coating method, with a coating amount controlled at 15 g / m². 2 Adjust the roller speed to 28 r / min and the coating pressure to 0.25 MPa to ensure that the coating liquid forms a uniform film on the surface of the biodegradable paper substrate. After coating, transfer the biodegradable paper substrate to a constant temperature oven, maintain the air velocity in the oven at 0.9 m / s and the temperature at 95°C, and keep it at that temperature for 35 minutes. Then let it cool naturally to room temperature for 28 minutes. Finally, a chemical bonding layer with a thickness of about 2.5 μm is formed on the surface of the biodegradable paper substrate, which can resist the friction and pressure when coffee cups are stacked.

[0032] Considering the oil content of beverages such as coffee, PLA with a number average molecular weight of 90,000 and PLGA with a number average molecular weight of 70,000 were weighed at a mass ratio of 8.5:1.5, with the lactic acid-glycolic acid molar ratio of PLGA being 7.8:2.2. An organic solvent consisting of dichloromethane and N,N-dimethylformamide mixed at a volume ratio of 3:1 was selected, controlling the total mass ratio of the organic solvent to PLA+PLGA to be 4.5:1. PLA was first added to the organic solvent and stirred at 32°C for 38 minutes to dissolve. After the PLA was completely dissolved, PLGA was added and stirring continued for 75 minutes. The solution was observed periodically during this time to ensure no agglomeration of particles, ultimately forming a uniform and transparent composite coating solution. Figure 2 As shown, it is adapted to the process requirements of mass coating in coffee shops.

[0033] The composite coating solution was applied to the surface of the biodegradable paper substrate treated with the bridging agent using a spraying method, with the coating amount controlled at 40 g / m². 2 The spraying pressure was adjusted to 0.45 MPa, and the nozzle distance from the biodegradable paper substrate surface was 22 cm to ensure uniform coating thickness. The coated biodegradable paper substrate was then placed smoothly into a sealed reactor, and nitrogen gas was introduced to purge the air inside the reactor. The nitrogen gas introduction rate was maintained at 2.5 L / min, and the reactor temperature was raised to 130°C at a heating rate of 4°C / min. The polymerization pressure was controlled at 0.6 MPa, and the reaction was continued for 80 minutes. After the reaction, the temperature was lowered to room temperature at a rate of 4.5°C / min, forming a temperature-sensitive responsive composite coating with a thickness of about 9 μm on the surface of the chemically bonded layer. This temperature-sensitive responsive composite coating can quickly form a dense barrier structure when the beverage is at high temperature, preventing oil penetration.

[0034] Biodegradable paper substrate with a temperature-sensitive composite coating is cooled to room temperature and cut to standard dimensions for chain coffee shops: top diameter 8.5cm, bottom diameter 5.2cm, and height 11cm, with a 2mm allowance for edge curling at the rim. The cups are then fed into a paper cup molding machine, with a molding temperature of 95℃ and a pressure of 1.8MPa, held for 18 minutes. During molding, anti-slip textures are incorporated into the cup body to accommodate consumer grip. After molding, the paper cups are placed in a vacuum drying oven and dried at 75℃ and a vacuum of -0.095MPa for 22 hours. Ventilation is provided every 6 hours for 19 minutes during drying to thoroughly remove residual solvents. The final product is an environmentally friendly PLA-coated hot beverage cup suitable for use in coffee shops, meeting consumers' needs for a cup that is not too hot to hold and does not leak when filled with coffee.

[0035] In summary, to meet the serving needs of hot beverages such as freshly ground coffee, a high-stiffness biodegradable paper substrate is selected, combined with a compounded bio-based coupling bridging agent to form a stable chemical bond layer, and then a temperature-sensitive composite coating is constructed by in-situ polymerization of PLA and PLGA. This ensures a strong bond between the coating and the substrate, and forms a dense barrier structure at coffee temperatures. The finished hot beverage cup meets the needs of store operations for high-frequency stacking and storage and quick dispensing, as well as the needs of consumers for holding the cup without burning their hands and for long-term use without leakage. At the same time, the entire system uses biodegradable components, fully retaining its environmental protection attributes, and is suitable for large-scale application in coffee shops.

[0036] Example 2:

[0037] Designed for the use of PLA-based hot beverage cups in the food delivery industry, this PLA-based hot beverage cup can hold hot soup, spicy hot pot broth, and other high-temperature, high-oil foods at 90-95℃. It must possess core properties such as compression resistance, leak-proofness, and high-temperature resistance. The specific manufacturing process is as follows: A high-toughness PLA substrate with a thickness of 0.45mm is selected. The PLA substrate can withstand collisions and compression during food delivery. The surface of the substrate is repeatedly wiped with a lint-free cloth soaked in anhydrous ethanol to remove residual oil and mold impurities from the production process. After wiping, the PLA substrate is placed in a vacuum drying oven and dried at 58℃ for 1.4 hours to ensure no moisture residue remains on the surface. Subsequently, the dried PLA substrate is placed in a continuous hot air preheating oven, with a preheating temperature set at 108℃ for 50 minutes to release the internal stress generated during substrate processing, preventing warping and deformation during subsequent molding, and further activating surface-active groups.

[0038] A lignin-based coupling agent was selected as the bio-based coupling bridging agent. This lignin-based coupling agent exhibits better compatibility with PLA substrates and is soluble in anhydrous ethanol. The mixture was stirred at 380 rpm for 22 minutes to prepare a 10% (w / w) bridging agent solution. The bridging agent solution was then sprayed onto the surface of the pretreated PLA substrate, with a coating amount controlled at 10 g / m². 2 Adjust the spraying pressure to 0.35MPa and the nozzle distance to the PLA substrate surface to 18cm to ensure uniform coverage of the PLA substrate surface. After coating, place the PLA substrate in a constant temperature oven, maintain the air velocity in the oven at 0.7m / s and the temperature at 88℃, and keep it at that temperature for 32 minutes. Then allow it to cool naturally to room temperature for 24 minutes. This will form a chemical bonding layer with a thickness of about 1.8μm on the PLA substrate surface, which can enhance the adhesion between the coating and the PLA substrate and resist vibration during food delivery.

[0039] To address the barrier requirements of high-temperature, high-fat foods, PLA with a number-average molecular weight of 70,000 and PLGA with a molar ratio of lactic acid-glycolic acid of 7.2:2.8 and a number-average molecular weight of 60,000 were weighed at a mass ratio of 7.8:2.2. An organic solvent consisting of dichloromethane and acetone mixed at a volume ratio of 4:1 was selected, and the total mass ratio of the organic solvent to PLA+PLGA was controlled at 6.5:1. PLA was first added to the organic solvent and stirred and dissolved at 29°C for 35 minutes until it reached a homogeneous state. Then, PLGA was added and stirring was continued for 85 minutes to ensure complete fusion of the two components, ultimately forming a composite coating solution with strong stability and suitable for high-temperature environments.

[0040] The composite coating liquid was applied to the surface of the PLA substrate treated with the bridging agent using a roller coating method, with the coating amount controlled at 32 g / m². 2 The roller speed was adjusted to 32 r / min and the coating pressure to 0.35 MPa to ensure no sagging of the coating on the PLA substrate surface. The coated PLA substrate was then fed into a reactor, and nitrogen gas was introduced to purge air from the reactor, maintaining a nitrogen introduction rate of 1.8 L / min. The reactor temperature was raised to 120°C at a heating rate of 3°C / min, and the polymerization pressure was controlled at 0.5 MPa, with the reaction continuing for 95 minutes. After the reaction, the temperature was lowered to room temperature at a rate of 3.8°C / min, forming a temperature-sensitive composite coating with a thickness of approximately 8 μm. Figure 3 As shown, it can quickly densify in high-temperature food environments, effectively preventing the penetration of broth and heat loss.

[0041] The cooled PLA substrate is cut into cup blanks with a top diameter of 10cm, a bottom diameter of 6cm, and a height of 13cm according to the requirements of takeout food packaging. The cup bottom is designed with a thickened structure to enhance load-bearing capacity. Then, it is sent into a plastic cup molding machine, with the molding temperature set at 92℃ and the pressure at 1.6MPa, and the pressure held for 16 minutes. During the molding process, the cup body is reinforced with ribs to improve its resistance to compression. After molding, the hot beverage cup is placed in a vacuum drying oven and dried for 21 hours at 68℃ and a vacuum degree of -0.088MPa. During the drying process, ventilation is carried out for 17 minutes every 6 hours to completely remove residual solvents. The final product is an environmentally friendly PLA-coated hot beverage cup suitable for high-temperature takeout food, which can meet the requirements of high-temperature insulation, no leakage, and no coating peeling during delivery.

[0042] In summary, high-toughness PLA substrate is selected to resist collisions and compression during delivery. The chemical bonding layer formed by the reaction of lignin-based coupling agent and active groups on the substrate surface enhances the adhesion stability of the subsequent temperature-sensitive composite coating. This composite coating can rapidly densify in high-temperature and high-oil environments, effectively preventing the penetration of hot soup and other food items and heat loss. The molded hot beverage cup has enhanced compression resistance through thickened bottom and reinforced body design, meeting the requirements of heat preservation, leak prevention, and no coating peeling during food delivery. The fully biodegradable system also aligns with the green development trend of the food delivery industry.

[0043] Example 3:

[0044] For the use of biodegradable paper-based hot beverage cups in community convenience stores, these cups are suitable for holding various everyday hot beverages such as hot porridge, oden soup, and hot milk at 70-85℃. They need to meet the requirements of small capacity, easy stacking, suitability for convenience store shelf storage, and immediate consumption by consumers. The specific manufacturing process involves selecting a paper-based hot beverage cup with a weight of 200g / m³. 2 The lightweight biodegradable paper substrate combines portability and structural strength, making it suitable for multi-layer stacking on convenience store shelves without taking up too much space. Low-pressure deionized water spraying is used to clean residual production impurities and dust from the surface. After cleaning, it is quickly placed in a vacuum drying oven and dried at 62°C for 1.6 hours, strictly controlling the moisture content of the biodegradable paper substrate. Subsequently, the dried biodegradable paper substrate is laid flat on a single-layer material rack and preheated in a constant-temperature oven at 105°C for 35 minutes. This thoroughly removes trace amounts of bound water from the biodegradable paper substrate while preventing it from becoming brittle due to high temperatures. Simultaneously, it activates surface-active groups, laying a solid foundation for subsequent bridging reactions.

[0045] A bio-based coupling bridging agent was selected by compounding polylactic acid diisocyanate and lignin-based coupling agent at a mass ratio of 1:1. This compounding ratio balances cost and adhesion, making it suitable for bulk purchases by convenience stores. The bridging agent was dissolved in anhydrous ethanol and stirred at 320 rpm for 18 minutes to prepare an 8% (w / w) bridging agent solution. The bridging agent solution was then uniformly coated onto the pretreated biodegradable paper substrate surface using a spraying method, with the coating amount controlled at 10 g / m². 2 Adjust the spraying pressure to 0.25MPa and the nozzle distance to the biodegradable paper substrate surface to ensure the formation of a thin and uniform film on the biodegradable paper substrate surface to avoid waste; after coating, transfer the biodegradable paper substrate to a constant temperature oven, maintain the air velocity in the oven at 0.6m / s and the temperature at 85℃, keep it at this temperature for 28 minutes, and then let it cool naturally to room temperature for 23 minutes. Finally, a chemical bonded layer with a thickness of about 1.8μm is formed on the surface of the biodegradable paper substrate, which can resist the slight collisions and friction when stacking convenience store shelves.

[0046] To address the significant variations in oil content in hot beverages sold in convenience stores, PLA with a number-average molecular weight of 70,000 and PLGA with a molar ratio of 7.3:2.7 (lactic-co-glycolic acid: acetic acid) and a number-average molecular weight of 55,000 were weighed at a mass ratio of 7:3. An organic solvent consisting of dichloromethane and acetone mixed at a volume ratio of 4:1 was selected, and the total mass ratio of the organic solvent to PLA+PLGA was controlled at 7:1. PLA was first added to the organic solvent and stirred at 27°C for 33 minutes until completely dissolved. After the PLA was completely dissolved, PLGA was added and stirring continued for 68 minutes. During this process, the solution transparency was observed to determine the dissolution status, ensuring no visible agglomerates were present. This resulted in a highly stable composite coating solution compatible with various coating equipment, meeting the diverse production needs of convenience store cups.

[0047] The composite coating solution is applied to the surface of the biodegradable paper substrate treated with a bridging agent using a roller coating method, with the coating amount controlled at 25 g / m². 2 The roller speed was adjusted to 22 r / min and the coating pressure to 0.2 MPa to ensure uniform coating thickness and no sagging. The coated biodegradable paper substrate was then placed smoothly into a sealed reactor. Nitrogen gas was introduced to purge the air from the reactor, maintaining a nitrogen introduction rate of 1.2 L / min. The reactor temperature was raised to 118°C at a heating rate of 2.5°C / min, and the polymerization pressure was controlled at 0.4 MPa. The reaction was continued for 105 minutes. After the reaction, the temperature was lowered to room temperature at a rate of 3.2°C / min, forming a temperature-sensitive composite coating with a thickness of approximately 6 μm on the surface of the chemically bonded layer. This temperature-sensitive composite coating can quickly form a suitable barrier structure under different hot beverage environments, effectively preventing the penetration of oil and water from hot porridge, oden soup, etc.

[0048] Biodegradable paper substrate with a temperature-sensitive composite coating is cooled to room temperature and cut to the standard size of small-capacity hot beverage cups for convenience stores: 7cm top diameter, 4.5cm bottom diameter, and 9cm height. The cup rim is designed with rounded edges to prevent scratching consumers' lips. The cups are then fed into a paper cup molding machine, with a molding temperature of 88℃ and a pressure of 1.3MPa, held for 13 minutes. During molding, the cup body is designed with fine, non-slip stripes for easy grip and to meet the sealing requirements of convenience store lids. After molding, the paper cups are placed in a vacuum drying oven and dried at 65℃ and a vacuum of -0.085MPa for 16 hours. During the drying process, ventilation is carried out for 16 minutes every 6 hours to completely remove residual solvents. The final product is an environmentally friendly PLA-coated hot beverage cup suitable for community convenience stores, meeting the needs of consumers for immediate consumption, preventing deformation during convenience store shelf storage, and preventing leakage when holding different hot beverages.

[0049] In summary, a lightweight, biodegradable paper substrate is used to adapt to multi-layer stacking storage on shelves. A chemical bonding layer is constructed through a 1:1 compounded bio-based coupling bridging agent. Combined with a composite coating liquid prepared by PLA and PLGA, a temperature-sensitive responsive composite coating is formed through in-situ polymerization. This coating can meet the barrier requirements of hot beverages with different oil contents, such as hot porridge and oden soup. The molded small-capacity hot beverage cup has a rounded edge and anti-slip stripe design, which takes into account both safety and convenience. It can meet consumers' needs for immediate drinking, and can be stored on convenience store shelves for a long time without deformation. Its fully biodegradable characteristics also meet the environmental protection requirements of daily consumption.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup, characterized in that, The specific steps of this method are as follows: Substrate pretreatment: Select biodegradable paper substrate or PLA substrate, and preheat it after cleaning and drying; Bridging agent coating: The bio-based coupling bridging agent is dissolved in anhydrous ethanol to prepare a bridging agent solution, which is then coated on the surface of the pretreated biodegradable paper substrate or PLA substrate, and a chemical bonding layer is formed after heat preservation. Preparation of composite coating solution: Weigh PLA and PLGA, add organic solvent and stir to dissolve to form composite coating solution; In-situ polymerization reaction: The composite coating liquid is applied to the surface of the biodegradable paper substrate or PLA substrate after being coated with the bridging agent solution, and then placed in a reaction vessel and nitrogen gas is introduced to carry out the in-situ polymerization reaction to form a temperature-sensitive composite coating. Post-molding treatment: The biodegradable paper substrate or PLA substrate with the temperature-sensitive composite coating is cooled to room temperature, cut, molded and then vacuum dried to obtain an environmentally friendly PLA-coated high-temperature and oil-resistant hot beverage cup.

2. The method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup according to claim 1, characterized in that, In the substrate pretreatment, the biodegradable paper substrate is cleaned with deionized water, and the PLA substrate is wiped with anhydrous ethanol. After cleaning, the biodegradable paper substrate or PLA substrate is dried in a vacuum drying oven. The preheating temperature of the biodegradable paper substrate or PLA substrate after drying is 100-120℃, and the preheating time is 30-60 minutes.

3. The method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup according to claim 2, characterized in that, In the substrate pretreatment, the biodegradable paper substrate is dried in a vacuum drying oven at a temperature of 60-70℃ for 1.5-2 hours; the PLA substrate is dried in a vacuum drying oven at a temperature of 50-60℃ for 1-1.5 hours.

4. The method for preparing an environmentally friendly PLA-coated high-temperature and grease-resistant hot beverage cup according to claim 1, characterized in that, In the bridging agent coating process, the bio-based coupling bridging agent is one or a combination of two of polylactic acid diisocyanate and lignin-based coupling agent. When the combination is made up, the mass ratio of polylactic acid diisocyanate to lignin-based coupling agent is 1:1-3:

1. When the compounded bio-based coupling bridging agent is dissolved, the stirring rate is 300-500 r / min, the stirring time is 15-30 min, and the mass concentration of the bridging agent solution is 5-15%.

5. The method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup according to claim 1, characterized in that, In the bridging agent coating process, the bridging agent solution is applied by spraying or roller coating, with a coating amount of 5-20 g / m². 2 When selecting roller coating, the roller speed is 20-30 r / min and the coating pressure is 0.1-0.3 MPa; when selecting spray coating, the spraying pressure is 0.2-0.4 MPa and the nozzle distance is 15-25 cm from the surface of the pretreated biodegradable paper substrate or PLA substrate.

6. The method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup according to claim 1, characterized in that, In the bridging agent coating process, the heat preservation process is carried out in a constant temperature oven with an air velocity of 0.5-1 m / s, a heat preservation temperature of 80-100℃, and a heat preservation time of 20-40 min. After the heat preservation is completed, the temperature is allowed to drop naturally to room temperature for 20-30 min. The chemical bonding layer is a thin film formed by the reaction of a bio-based coupling bridging agent with surface active groups of a biodegradable paper substrate or PLA substrate, with a thickness of 1-3 μm.

7. The method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup according to claim 1, characterized in that, In the preparation of the composite coating solution, the mass ratio of PLA to PLGA is 7:3-9:1, the number average molecular weight of PLA is 50,000-100,000, the molar ratio of lactic acid to glycolic acid of PLGA is 7:3-8:2, and the number average molecular weight is 40,000-80,000; the organic solvent is a mixed solvent of dichloromethane and N,N-dimethylformamide at a volume ratio of 3:1, or a mixed solvent of dichloromethane and acetone at a volume ratio of 4:1, and the total mass ratio of the organic solvent to PLA+PLGA is 3.6:1-9:1; PLA is first added to the organic solvent and dissolved for 30-40 minutes, then PLGA is added and the stirring continues to dissolve, the stirring temperature is 25-35℃, and the stirring time is 60-90 minutes.

8. The method for preparing an environmentally friendly PLA-coated high-temperature and grease-resistant hot beverage cup according to claim 1, characterized in that, In the in-situ polymerization reaction, the coating amount of the composite coating solution is 20-50 g / m³. 2 The coating method is either spraying or roller coating. When roller coating is selected, the roller speed is 25-35 r / min and the coating pressure is 0.2-0.4 MPa. When spraying is selected, the spraying pressure is 0.3-0.5 MPa and the nozzle distance from the surface of the biodegradable paper substrate or PLA substrate is 20-30 cm.

9. The method for preparing an environmentally friendly, high-temperature resistant, and grease-resistant PLA-coated hot beverage cup according to claim 1, characterized in that, In the in-situ polymerization reaction, the temperature inside the reactor is 110-140℃, the polymerization pressure is 0.3-0.8MPa, and the reaction time is 60-120min; the nitrogen gas introduction rate is 1-3L / min, the reactor heating rate is 2-5℃ / min, and the cooling rate after the reaction is completed is 3-5℃ / min; the temperature-sensitive composite coating is a composite layer formed by the in-situ polymerization reaction of PLA and PLGA, with a thickness of 5-10μm.

10. The method for preparing an environmentally friendly PLA-coated high-temperature resistant and grease-resistant hot beverage cup according to claim 1, characterized in that, In the post-molding treatment, the molding temperature is 80-100℃, the molding pressure is 1-2MPa, and the holding time is 10-20min; the vacuum drying temperature is 60-80℃, the drying time is 12-24h, and the vacuum degree is -0.08 to -0.1MPa; during the drying process, ventilation is carried out once every 6 hours, and each ventilation lasts for 15-20min.

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