Environment-friendly film for milk tea heat preservation bag and preparation process of environment-friendly film

Abstract

The invention discloses an environment-friendly film for a milk tea heat preservation bag and a preparation process of the environment-friendly film. In the invention, the inner functional adsorption layer adopts a partitioned design of a core adsorption area and an auxiliary adsorption area, the core area takes linear low-density polyethylene as a base material and is matched with high-proportion food-grade diatomite and modified activated carbon, and liquid and sugar generated during milk tea leakage can be quickly captured by utilizing porous structures and microporous adsorption capacities of the two; liquid is prevented from remaining on the film surface; in the auxiliary adsorption area, the flexibility of the film layer is improved through a proper amount of thermoplastic elastomer, meanwhile, dispersed trace liquid is subjected to secondary adsorption in cooperation with a small amount of adsorbent, and the outer barrier layer takes polyethylene glycol terephthalate as a main body and is supplemented with linear low-density polyethylene to enhance the interlayer binding force; the influence of external moisture and temperature change on the adsorption effect in the film can be blocked, the overall structural strength of the film material can be kept, deformation or damage caused by liquid adsorption is avoided, and the sticky feeling when the hand touches the film is fundamentally reduced.

Description

Technical Field

[0001] This invention belongs to the field of beverage packaging technology, specifically an environmentally friendly film for milk tea insulated bags and its preparation process. Background Technology

[0002] Insulated milk tea bags are portable, functional packaging designed specifically to maintain the temperature of beverages. They are typically composed of an outer abrasion-resistant fabric, a middle insulation layer, and an inner waterproof and impermeable material. Their core principle is to effectively slow heat loss through the air insulation layer (such as pearl cotton, EPE, or aluminum foil bubble wrap), thus keeping hot drinks like milk tea and coffee warm in winter or cold drinks in summer. These products usually come with handles or zippers for easy carrying and spill prevention, and have become common consumer accessories for takeout delivery, office afternoon tea, and daily travel, meeting the dual demands of instant taste and convenience in today's fast-paced lifestyle. With the rapid development of the freshly made tea beverage industry, insulated milk tea bags, as an important packaging option for beverage takeout, have received widespread attention for their user experience and environmental performance. Currently, most insulated milk tea bags on the market use films made of single-substrate materials such as polyethylene (PE) and polypropylene (PP) or simple composite structures, typically only providing basic insulation and barrier functions, and primarily using ordinary plastics as the material selection.

[0003] However, with traditional insulated milk tea bags, once the milk tea spills and dries over time, an adhesive layer forms on the inner wall of the bag. This results in a sticky feeling when hands come into contact with the bag's inner wall, negatively impacting the user experience and potentially posing a hygiene risk due to residual sugar and bacterial growth. Summary of the Invention

[0004] The purpose of this invention is to provide an environmentally friendly film for milk tea insulated bags and its preparation process in order to solve the problems mentioned above.

[0005] The technical solution adopted in this invention is as follows: an environmentally friendly film for milk tea insulated bags, comprising: an outer barrier layer and an inner functional adsorption layer;

[0006] The internal functional adsorption layer includes: a core adsorption region and an auxiliary adsorption region;

[0007] The outer barrier layer includes:

[0008] Polyethylene terephthalate: as the main substrate, with a mass fraction ranging from 85% to 95%;

[0009] Linear low-density polyethylene: used as an interlayer bonding component, with a mass fraction ranging from 3% to 7%;

[0010] Food-grade slip agent: mass fraction range of 1%-3%;

[0011] Antioxidant: mass fraction range of 0.3% to 0.7%;

[0012] Food-grade color masterbatch: mass fraction range of 0.3% to 0.7%.

[0013] The core adsorption region of the internal functional adsorption layer includes:

[0014] Linear low-density polyethylene: used as the main substrate, with a mass fraction ranging from 70% to 80%;

[0015] Food-grade diatomaceous earth: as the main adsorbent for capturing sugars with a porous structure, with a mass fraction range of 15% to 22%;

[0016] Food-grade modified activated carbon: used as an auxiliary adsorbent to enhance the adsorption capacity of micropores, with a mass fraction ranging from 5% to 8%;

[0017] The auxiliary adsorption region of the internal functional adsorption layer includes:

[0018] Linear low-density polyethylene: used as the main substrate, with a mass fraction ranging from 85% to 95%;

[0019] Thermoplastic elastomer: mass fraction range of 3% to 7%;

[0020] Food-grade diatomaceous earth: mass fraction range of 3% to 6%;

[0021] Food-grade modified activated carbon: mass fraction range of 1% to 2%.

[0022] In a preferred embodiment, a process for preparing an environmentally friendly film for milk tea insulated bags includes the following steps:

[0023] S1: Raw material pretreatment and mixing preparation. First, the polyethylene terephthalate, linear low-density polyethylene, food-grade slip agent, antioxidant, and food-grade color masterbatch required for the outer barrier layer are dried to control the moisture content to below 0.1%. At the same time, the food-grade diatomaceous earth and modified activated carbon of the inner functional adsorption layer are sieved to ensure uniform particle size distribution, laying the foundation for the subsequent mixing and molding of each layer of materials.

[0024] S2: Preparation of outer barrier layer substrate. Pretreated polyethylene terephthalate is added to a high-speed mixer at a ratio of 85%–95% with linear low-density polyethylene, slip agent, antioxidant, and color masterbatch. The mixture is stirred at 120–140°C for 20–30 minutes until homogeneous. Then, it is extruded and cast through a twin-screw extruder to obtain an outer barrier substrate film with a thickness of 15–20 μm for later use.

[0025] S3: Mixing of core adsorption zone materials. Based on the core adsorption zone formulation of the internal functional adsorption layer, linear low-density polyethylene, food-grade diatomaceous earth, and modified activated carbon are added to a mixer in proportion and stirred at 110-130℃ for 30-40 minutes. During this period, ultrasonic dispersion is used to assist in the uniform dispersion of the adsorbent, ensuring that there is no agglomeration in the mixed system, thus preparing for the subsequent formation of the core zone membrane.

[0026] S4: Mixing of auxiliary adsorption zone materials. Simultaneously process the auxiliary adsorption zone materials of the internal functional adsorption layer. Add linear low-density polyethylene, thermoplastic elastomer, food-grade diatomaceous earth, and modified activated carbon in proportion to another mixer and stir at low speed at 100-120℃ for 25-35 minutes. Utilize the compatibilizing effect of thermoplastic elastomer to improve the system compatibility and obtain the auxiliary adsorption zone mixture.

[0027] S5: Internal functional adsorption layer partitioning. Using a co-extrusion die, the core adsorption zone mixture prepared in S3 and the auxiliary adsorption zone mixture prepared in S4 are fed into two independent flow channels of the die. Through the partitioning control of the die head, the core adsorption zone material is formed in the central area at the bottom of the die, and the auxiliary adsorption zone material is formed in the side and top areas of the die. They are co-extruded and cast into an internal functional adsorption substrate film with a thickness of 20-25μm.

[0028] S6: Processing of the inner layer microgroove structure. When the inner functional adsorption substrate film obtained in S5 cools to 60-70℃, it is sent to the molding equipment and molded through the preset radial groove template to form a flow-guiding groove on the surface of the inner layer film, which converges from the edge of the bag opening and the middle of the side to the bottom center. After the process is completed, it is naturally cooled to room temperature to enhance the subsequent liquid flow guiding effect.

[0029] S7: Inner and outer layer composite molding. The outer barrier substrate film prepared in S2 is aligned with the inner functional adsorption substrate film treated in S6, and fed into a laminating machine. The two films are then laminated together using a hot-pressing process to ensure a lamination strength of 2.5N / 15mm or higher, forming a complete environmentally friendly membrane substrate.

[0030] S8: Post-processing and slitting. The composite film obtained in S7 is cured to eliminate internal stress and improve interlayer bonding. Then, according to the size requirements of the milk tea insulated bag, it is slitting into film sheets of specific specifications using a slitting machine, finally obtaining an environmentally friendly film product that can be used to make milk tea insulated bags.

[0031] In a preferred embodiment, in step S1, the polyethylene terephthalate, linear low-density polyethylene, food-grade slip agent, antioxidant, and food-grade masterbatch required for the outer barrier layer are first dried. Residual moisture in the materials is removed using a hot air circulating dryer, controlling the moisture content to a low level to prevent bubbles or pinholes from forming during subsequent processing due to moisture evaporation. The food-grade diatomaceous earth and modified activated carbon of the inner functional adsorption layer are mechanically sieved, separating particles with uniform particle size distribution through multiple layers of sieves. This removes large impurities and ultrafine dust, ensuring uniform dispersion of the adsorbent during subsequent mixing and laying the foundation for the molding quality of each layer.

[0032] In a preferred embodiment, in step S2, the preparation of the outer barrier layer substrate requires strict control of mixing and extrusion parameters to ensure the mechanical properties and barrier properties of the film. The dried polyethylene terephthalate, linear low-density polyethylene, slip agent, antioxidant, and color masterbatch are added to a high-speed mixer according to the main proportion. The mixer speed is set to 800-1000 rpm, heated to 125-135 degrees Celsius, and continuously stirred for 25-30 minutes to ensure thorough melting and dispersion of the components. After mixing, the material is fed into a twin-screw extruder at a rate of 20-25 kg / h via a feeder. The temperatures of each zone of the extruder are controlled sequentially as follows: Zone 1: 170-180 degrees Celsius; Zone 2: 185-195 degrees Celsius; Zone 3: 200-210 degrees Celsius; Die head temperature: 205-215 degrees Celsius. The screw speed is adjusted to 150-180 rpm, further homogenizing the material through the shearing and conveying action of the screw. The molten material is extruded through a T-shaped casting die, with the die lip gap set at 0.3–0.4 mm. The casting roller temperature is controlled at 25–35 degrees Celsius, and the cooling rate is 8–10 degrees Celsius per second. The final outer barrier substrate film with a thickness of 15–20 micrometers is formed. The winding tension is maintained at 5–8 Newtons to ensure that the film surface is flat and wrinkle-free.

[0033] In a preferred embodiment, during step S3, the equipment temperature is controlled to the range where the substrate begins to melt, the stirring device is activated to allow the materials to slowly fuse, and the ultrasonic dispersion auxiliary system is simultaneously activated to break up agglomeration between adsorbent particles using high-frequency vibration, ensuring that diatomaceous earth and modified activated carbon are uniformly dispersed in the polyethylene substrate. The entire mixing process needs to continue for a sufficient duration until sampling confirms that there is no significant agglomeration of the adsorbent, forming a uniformly dispersed mixed system, which provides a guarantee for the subsequent formation of the core membrane layer and its adsorption performance.

[0034] In a preferred embodiment, in step S4, while the materials in the core adsorption zone are being mixed, another mixing device is started to process the materials in the auxiliary adsorption zone. Linear low-density polyethylene is used as the main substrate, and thermoplastic elastomer, food-grade diatomaceous earth, and modified activated carbon are added in proportion. The equipment temperature is controlled to a range where the thermoplastic elastomer softens but does not decompose. A low stirring speed is used for mixing to avoid high-speed shearing that could cause the elastomer molecular chains to break.

[0035] In a preferred embodiment, in step S5, the core adsorption zone mixture and the auxiliary adsorption zone mixture are respectively fed into two independent channels of the co-extrusion die. The temperature of the core adsorption zone channel is set to 160-170 degrees Celsius, and the temperature of the auxiliary adsorption zone channel is set to 155-165 degrees Celsius. The overall die head temperature is controlled at 165-175 degrees Celsius. The material flow ratio between the core zone and the auxiliary zone is adjusted to 1:4 through the channel distribution system to ensure that the core adsorption zone accounts for 20% of the inner film area and the auxiliary adsorption zone accounts for 80% after molding. After the molten material is extruded through the die head, it enters the casting cooling roller at a speed of 0.8-1.2 meters per minute. The temperature of the cooling roller is controlled at 30-40 degrees Celsius, and the cooling time is 15-20 seconds to quickly solidify the film layer. The total thickness of the molded internal functional adsorption substrate film is controlled at 20-25 micrometers, with the core adsorption zone thickness slightly higher than the auxiliary adsorption zone to ensure a balance between adsorbent content and structural stability.

[0036] After mixing the core and auxiliary adsorption zone materials, the internal functional adsorption layer is formed in sections. The two mixed materials are fed into two independent channels of a co-extrusion die. According to design requirements, the die has channel outlets corresponding to the core adsorption zone in the bottom center area, and channel outlets corresponding to the auxiliary adsorption zones in the side and top areas. By adjusting the temperature and pressure of each zone of the die, the two materials are kept in a suitable molten state within the die. After co-extrusion and casting, the mixture is cooled and formed, creating an internal functional adsorption substrate film with the core adsorption zone at the bottom center and the remaining areas as auxiliary adsorption zones. During the forming process, it is essential to ensure that the materials in the two zones are fully fused at the interface, without obvious delamination or gaps, to guarantee the integrity of the overall film structure.

[0037] In a preferred embodiment, in step S6, after the internal functional adsorption substrate film is formed, the inner layer microgroove structure is immediately processed. The film layer, cooled to a certain temperature, is fed into a molding equipment. At this time, the film layer needs to be kept in an appropriate softened state to ensure that a clear groove structure can be imprinted by the template. The template surface in the molding equipment is provided with a preset radial groove pattern. By applying uniform pressure, the template is brought into close contact with the film surface, and a guide groove converging from the edge to the bottom center is imprinted on the film surface.

[0038] In a preferred embodiment, step S7, the inner and outer layer lamination is a crucial step determining the overall performance of the environmentally friendly membrane, requiring control of interlayer bonding force and membrane surface quality through hot-pressing parameters. After aligning the outer barrier substrate membrane and the inner functional adsorption substrate membrane, they are fed into the laminating machine. The temperature of the hot-pressing rollers of the laminating machine is set to 135–145 degrees Celsius, the pressure is adjusted to 0.35–0.45 MPa, and the lamination speed is controlled at 1.5–2 meters per minute to ensure full fusion of the two membranes under hot-pressing. During the lamination process, the tension of the outer membrane is maintained at 6–8 Newtons and the tension of the inner membrane at 4–6 Newtons through a tension control system to prevent membrane stretching and deformation. After lamination, an online peel strength test is immediately performed to ensure that the lamination strength reaches at least 2.5–3 Newtons per 15 millimeters. The composite film is then placed in a curing chamber, with a curing temperature of 45–50 degrees Celsius, a relative humidity of 40%–50%, and a curing time of 28–32 hours. The slow curing process eliminates internal stress and further enhances the interlayer bonding strength, ultimately resulting in a smooth, bubble-free composite film substrate.

[0039] In a preferred embodiment, in step S8, after the composite film is formed, post-processing is required to improve stability and meet bag-making requirements. The composite film is sent to a curing chamber and placed at a mild temperature for a sufficient time. The curing process eliminates the internal stress generated during processing, promotes further diffusion and fusion of interlayer molecules, and improves interlayer bonding and overall film smoothness. After curing, the composite film is sent to a slitting machine. According to the design size requirements of the milk tea insulated bag, the film roll is slitted into film sheets of specific specifications using a high-precision slitting device. The cutting accuracy must be controlled during the slitting process to ensure that the edges of the film sheets are neat and burr-free, ultimately obtaining an environmentally friendly finished film that can be directly used to make milk tea insulated bags.

[0040] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0041] 1. In this invention, the inner functional adsorption layer adopts a partitioned design of a core adsorption zone and an auxiliary adsorption zone. The core zone uses linear low-density polyethylene as the substrate, combined with a high proportion of food-grade diatomaceous earth and modified activated carbon. Utilizing the porous structure and microporous adsorption capacity of these two materials, it can quickly capture the liquid and sugar generated when milk tea leaks, preventing liquid residue on the membrane surface. The auxiliary adsorption zone enhances the membrane's flexibility with an appropriate amount of thermoplastic elastomer, while simultaneously using a small amount of adsorbent to perform secondary adsorption of dispersed trace amounts of liquid, forming a dual guarantee of "strong core adsorption + auxiliary micro-capture". The outer barrier layer is mainly composed of polyethylene terephthalate, supplemented with linear low-density polyethylene to enhance interlayer bonding. This not only blocks the influence of external moisture and temperature changes on the adsorption effect inside the membrane but also maintains the overall structural strength of the membrane material, preventing deformation or damage after liquid adsorption, and fundamentally reducing the sticky feeling when touching the surface.

[0042] 2. In this invention, the environmentally friendly film achieves an anti-sticking function while also ensuring material safety and process stability. All raw materials are food-grade. Adsorbents such as diatomaceous earth and modified activated carbon have natural environmental protection properties, and the substrate, such as linear low-density polyethylene, is easy to process and meets food contact standards. It does not release harmful substances during use and can be naturally degraded or recycled after disposal, meeting environmental protection requirements. In the manufacturing process, raw material pretreatment ensures uniform dispersion of each component, co-extrusion partitioning ensures precise bonding between the core and auxiliary adsorption areas, microgroove structures guide liquid to converge towards the core adsorption area, and the composite process strengthens the bonding strength between the inner and outer layers. This allows the film to maintain good flexibility and durability while possessing adsorption capabilities, making it suitable for repeated use in milk tea insulated bags and reducing environmental burden after disposal, thus comprehensively improving the product's user experience and environmental value. Attached Figure Description

[0043] Figure 1 This is a schematic diagram illustrating the process principle of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] Reference Figure 1 ,

[0046] Example:

[0047] An environmentally friendly film for insulated milk tea bags includes: an outer barrier layer and an inner functional absorbent layer;

[0048] The internal functional adsorption layer includes: a core adsorption region and an auxiliary adsorption region;

[0049] The outer barrier layer's core functions are to provide mechanical strength, barrier properties (preventing oxygen and moisture penetration), and printability. Its composition and mass fraction range are as follows:

[0050] Polyethylene terephthalate: As the main substrate, its mass fraction ranges from 85% to 95%, giving the film excellent tensile strength and barrier properties;

[0051] Linear low-density polyethylene: As an interlayer bonding component, its mass fraction ranges from 3% to 7%, which improves the composite strength between the outer and inner layers;

[0052] Food-grade slip agent: with a mass fraction range of 1% to 3%, reduces the surface friction coefficient and prevents packaging from sticking together when stacked;

[0053] Antioxidant: with a mass fraction ranging from 0.3% to 0.7%, inhibiting thermal oxidative degradation during material processing;

[0054] Food-grade masterbatch: with a mass fraction ranging from 0.3% to 0.7%, it provides a base color (such as white or transparent) to meet printing requirements.

[0055] II. Internal Functional Adsorption Layer:

[0056] The inner functional adsorption layer is the inner layer that contacts the food, including: a core adsorption zone (bottom center, for efficient adsorption of concentrated sugar water) and auxiliary adsorption zones (sides and top, balancing flexibility and auxiliary adsorption). Specific components and mass fraction ranges are as follows:

[0057] Core adsorption region:

[0058] Achieving efficient sugar capture with a high proportion of adsorbent, while ensuring basic mechanical properties through the substrate. Composition and scope:

[0059] Linear low-density polyethylene (LLDPE): As the main substrate, with a mass fraction ranging from 70% to 80%, it provides heat sealability and processing adaptability;

[0060] Food-grade diatomaceous earth: used as the main adsorbent (porous structure to capture sugars), with a mass fraction range of 15% to 22%;

[0061] Food-grade modified activated carbon: used as an auxiliary adsorbent (to enhance microporous adsorption capacity), with a mass fraction range of 5% to 8%;

[0062] (2) Auxiliary adsorption zone

[0063] A low proportion of adsorbent is used to balance cost and auxiliary adsorption function, while elastic components are added to ensure overall flexibility. Composition and scope:

[0064] Linear low-density polyethylene (LLDPE): As the main substrate, with a mass fraction ranging from 85% to 95%, it provides basic flexibility and tensile strength;

[0065] Thermoplastic elastomers (TPEs, such as SEBS): improve material elasticity and prevent embrittlement after absorbing moisture; mass fraction range is 3% to 7%.

[0066] Food-grade diatomaceous earth: a low-proportion auxiliary adsorbent, with a mass fraction ranging from 3% to 6%;

[0067] Food-grade modified activated carbon: a low-proportion auxiliary adsorbent, with a mass fraction ranging from 1% to 2%.

[0068] A manufacturing process for an environmentally friendly film used in insulated milk tea bags, characterized by the following steps:

[0069] S1: Raw material pretreatment and mixing preparation. First, the polyethylene terephthalate, linear low-density polyethylene, food-grade slip agent, antioxidant, and food-grade color masterbatch required for the outer barrier layer are dried to control the moisture content to below 0.1%. At the same time, the food-grade diatomaceous earth and modified activated carbon of the inner functional adsorption layer are sieved to ensure uniform particle size distribution, laying the foundation for the subsequent mixing and molding of each layer of materials.

[0070] S2: Preparation of the outer barrier layer substrate. Pretreated polyethylene terephthalate (PET) is added to a high-speed mixer at a ratio of 85%–95% with linear low-density polyethylene (3%–7%), slip agent (1%–3%), antioxidant (0.3%–0.7%), and color masterbatch (0.3%–0.7%). The mixture is stirred at 120–140°C for 20–30 minutes until homogeneous. The mixture is then extruded and cast using a twin-screw extruder to obtain an outer barrier layer substrate film with a thickness of 15–20 μm, for later use.

[0071] S3: Mixing of core adsorption zone materials. Based on the core adsorption zone formulation of the internal functional adsorption layer, linear low-density polyethylene (70%–80%), food-grade diatomaceous earth (15%–22%), and modified activated carbon (5%–8%) are added to a mixer in proportion and stirred at 110–130℃ for 30–40 minutes. During this time, ultrasonic dispersion is used to assist in the uniform dispersion of the adsorbent, ensuring that there is no agglomeration in the mixed system, thus preparing for the subsequent formation of the core zone membrane.

[0072] S4: Mixing of auxiliary adsorption zone materials. Simultaneously process the auxiliary adsorption zone materials of the internal functional adsorption layer. Add linear low-density polyethylene (85%–95%), thermoplastic elastomer (3%–7%), food-grade diatomaceous earth (3%–6%), and modified activated carbon (1%–2%) to another mixer in a specific ratio. Stir at low speed for 25–35 minutes at 100–120°C. Utilize the compatibilizing effect of the thermoplastic elastomer to improve the system's compatibility, thus obtaining the auxiliary adsorption zone mixture.

[0073] S5: Internal functional adsorption layer partitioning. Using a co-extrusion die, the core adsorption zone mixture prepared in S3 and the auxiliary adsorption zone mixture in S4 are fed into two independent flow channels of the die. Through die head partitioning control, the core adsorption zone material is formed in the central area at the bottom of the die (accounting for 20% of the inner layer film area), and the auxiliary adsorption zone material is formed in the side and top areas of the die (accounting for 80%). They are co-extruded and cast into an internal functional adsorption substrate film with a thickness of 20-25μm.

[0074] S6: Processing of the inner layer microgroove structure. After the inner functional adsorption substrate film obtained in S5 cools to 60-70℃, it is sent to a molding equipment and molded through a preset radial groove template (depth 0.5-1mm, width 1-2mm) to form a flow guiding groove on the surface of the inner layer film, which converges from the edge of the bag opening and the middle of the side to the bottom center. After processing, it is naturally cooled to room temperature to enhance the subsequent liquid flow guiding effect.

[0075] S7: Inner and outer layer composite molding. The outer barrier substrate film (non-food contact surface) prepared in S2 is aligned with the inner functional adsorption substrate film (food contact surface) treated in S6, and fed into a laminating machine. The two films are laminated into one by hot pressing (temperature 130-150℃, pressure 0.3-0.5MPa) to ensure that the lamination strength reaches more than 2.5N / 15mm, forming a complete environmentally friendly film substrate.

[0076] S8: Post-processing and slitting. The composite film obtained in S7 is subjected to a curing treatment (placed at 40-50℃ for 24-36 hours) to eliminate internal stress and improve interlayer bonding. Then, according to the size requirements of the milk tea insulated bag, it is slitting into film sheets of specific specifications using a slitting machine to finally obtain an environmentally friendly film product that can be used to make milk tea insulated bags.

[0077] In step S1, the polyethylene terephthalate, linear low-density polyethylene, food-grade slip agent, antioxidant, and food-grade masterbatch required for the outer barrier layer are first dried. Residual moisture is removed from the materials using a hot air circulating dryer, controlling the moisture content to a low level to prevent bubbles or pinholes from forming during subsequent processing. Simultaneously, the food-grade diatomaceous earth and modified activated carbon for the inner functional adsorption layer are mechanically sieved. Multiple layers of sieves separate particles with uniform size distribution, removing large impurities and ultrafine dust, ensuring uniform dispersion of the adsorbent during subsequent mixing, thus laying the foundation for the molding quality of each layer.

[0078] In step S2, after the raw material pretreatment is completed, the preparation of the outer barrier layer substrate begins. Dried polyethylene terephthalate (PET) is used as the main substrate and added to a high-speed mixer along with linear low-density polyethylene (LDPE), slip agent, antioxidant, and color masterbatch in a specific ratio. During mixing, the material temperature is raised to a suitable range using a heating device, ensuring thorough contact between the components in a molten state. Simultaneously, a stirring device is activated and continuously stirred at a suitable speed for a period of time until a homogeneous molten mixture is formed. The mixed material is then fed into a twin-screw extruder, where it is further homogenized through the shearing and conveying action of the screws. Finally, it is extruded through a casting die, cooled, and a barrier layer substrate film of a certain thickness is obtained. This film must possess good tensile strength and barrier properties to meet subsequent lamination and application requirements.

[0079] The preparation of the outer barrier layer substrate requires strict control of mixing and extrusion parameters to ensure the mechanical properties and barrier function of the film. Dried polyethylene terephthalate (PET) is added to a high-speed mixer along with linear low-density polyethylene (LDPE), slip agent, antioxidant, and masterbatch in the main proportions. The mixer speed is set to 800-1000 rpm, and the mixture is heated to 125-135 degrees Celsius and continuously stirred for 25-30 minutes to ensure thorough melting and dispersion of the components. After mixing, the material is fed into a twin-screw extruder at a rate of 20-25 kg / h via a feeder. The temperatures of each zone of the extruder are controlled sequentially as follows: Zone 1: 170-180 degrees Celsius; Zone 2: 185-195 degrees Celsius; Zone 3: 200-210 degrees Celsius; Die head temperature: 205-215 degrees Celsius. The screw speed is adjusted to 150-180 rpm, further homogenizing the material through the shearing and conveying action of the screw. The molten material is extruded through a T-shaped casting die, with the die lip gap set at 0.3–0.4 mm. The casting roller temperature is controlled at 25–35 degrees Celsius, and the cooling rate is 8–10 degrees Celsius per second. The final outer barrier substrate film with a thickness of 15–20 micrometers is formed. The winding tension is maintained at 5–8 Newtons to ensure that the film surface is flat and wrinkle-free.

[0080] In step S3, according to the formulation requirements, linear low-density polyethylene is used as the main substrate, and food-grade diatomaceous earth and modified activated carbon are added in proportion and fed into a dedicated mixing device. During mixing, the equipment temperature is controlled to the range where the substrate begins to melt, and the stirring device is started to slowly fuse the materials. At the same time, the ultrasonic dispersion auxiliary system is activated to break up the agglomeration between adsorbent particles using high-frequency vibration, ensuring that the diatomaceous earth and modified activated carbon are uniformly dispersed in the polyethylene substrate. The entire mixing process needs to continue for a sufficient duration until sampling and observation confirm that there is no obvious agglomeration of the adsorbent, forming a uniformly dispersed mixed system, which provides a guarantee for the subsequent formation of the core membrane layer and its adsorption performance.

[0081] In step S4, while the materials in the core adsorption zone are being mixed, another mixing device is started to process the materials in the auxiliary adsorption zone. Linear low-density polyethylene is used as the main substrate, and thermoplastic elastomer, food-grade diatomaceous earth, and modified activated carbon are added in proportion. The equipment temperature is controlled to a range where the thermoplastic elastomer softens but does not decompose. A low stirring speed is used for mixing to avoid high-speed shearing that could break the elastomer molecular chains. During the mixing process, the thermoplastic elastomer gradually disperses into the polyethylene substrate, forming a mixed system with a small amount of adsorbent that combines flexibility and auxiliary adsorption capacity. It is necessary to ensure that the elastomer is evenly distributed to guarantee that the film layer after molding maintains a soft feel while providing auxiliary adsorption for the dispersed trace amounts of liquid.

[0082] In step S5, the partitioning and molding of the inner functional adsorption layer requires precise control of the flow channel distribution and molding conditions through a co-extrusion die to achieve the synergistic effect of the core adsorption zone and the auxiliary adsorption zone. The core adsorption zone mixture and the auxiliary adsorption zone mixture are fed into two independent flow channels of the co-extrusion die. The temperature of the core adsorption zone flow channel is set to 160–170 degrees Celsius, and the temperature of the auxiliary adsorption zone flow channel is set to 155–165 degrees Celsius. The overall die head temperature is controlled at 165–175 degrees Celsius. The material flow ratio between the core zone and the auxiliary zone is adjusted to 1:4 through the flow channel distribution system to ensure that after molding, the core adsorption zone occupies 20% of the inner layer film area, and the auxiliary adsorption zone occupies 80%. After the molten material is extruded through the die, it enters the casting cooling roller at a speed of 0.8 to 1.2 meters per minute. The temperature of the cooling roller is controlled at 30 to 40 degrees Celsius, and the cooling time is 15 to 20 seconds, so that the film layer can be quickly shaped. The total thickness of the formed internal functional adsorption substrate film is controlled at 20 to 25 micrometers, of which the thickness of the core adsorption area is slightly higher than that of the auxiliary adsorption area, to ensure the balance between adsorbent content and structural stability.

[0083] After mixing the core and auxiliary adsorption zone materials, the internal functional adsorption layer is formed in sections. The two mixed materials are fed into two independent channels of a co-extrusion die. According to design requirements, the die has channel outlets corresponding to the core adsorption zone in the bottom center area, and channel outlets corresponding to the auxiliary adsorption zones in the side and top areas. By adjusting the temperature and pressure of each zone of the die, the two materials are kept in a suitable molten state within the die. After co-extrusion and casting, the mixture is cooled and formed, creating an internal functional adsorption substrate film with the core adsorption zone at the bottom center and the remaining areas as auxiliary adsorption zones. During the forming process, it is essential to ensure that the materials in the two zones are fully fused at the interface, without obvious delamination or gaps, to guarantee the integrity of the overall film structure.

[0084] In step S6, after the internal functional adsorption substrate film is formed, the inner layer microgroove structure is immediately processed. The film layer, cooled to a certain temperature, is fed into a molding machine. At this time, the film layer needs to be kept in a suitable softened state to ensure that a clear groove structure can be imprinted by the template. The template surface in the molding machine has a preset radial groove pattern. By applying uniform pressure, the template is brought into close contact with the film surface, and a flow-guiding groove converging from the edge to the bottom center is imprinted on the film surface. After imprinting, the film layer is slowly cooled to room temperature to avoid shrinkage and deformation of the groove structure due to rapid cooling, ensuring uniform groove depth and width, and providing a stable path for subsequent liquid flow.

[0085] In step S7, the inner and outer layer lamination is a crucial step determining the overall performance of the environmentally friendly membrane. The interlayer bonding force and membrane surface quality must be controlled through hot-pressing parameters. After aligning the outer barrier substrate membrane and the inner functional adsorption substrate membrane, they are fed into the laminator. The temperature of the hot-pressing rollers of the laminator is set to 135–145 degrees Celsius, the pressure is adjusted to 0.35–0.45 MPa, and the lamination speed is controlled at 1.5–2 meters per minute to ensure full fusion of the two membranes under hot-pressing. During the lamination process, the tension of the outer membrane is maintained at 6–8 Newtons and the tension of the inner membrane at 4–6 Newtons through a tension control system to prevent membrane stretching and deformation. After lamination, an online peel strength test is immediately performed to ensure that the lamination strength reaches at least 2.5–3 Newtons per 15 mm. The laminated membrane is then sent to a curing chamber, with a curing temperature of 45–50 degrees Celsius, a relative humidity of 40%–50%, and a curing time of 28–32 hours. Slow curing eliminates internal stress and further improves the interlayer bonding force, ultimately resulting in a smooth, bubble-free laminated membrane substrate.

[0086] After the inner microgrooves are processed, the outer barrier layer and the inner functional adsorption layer are laminated. The non-food-contact surfaces of the outer barrier substrate film and the inner functional adsorption layer are aligned and fed into the laminating machine. The laminating machine raises the temperature to the heat-sealing temperature range of both substrates using heating rollers, while simultaneously applying uniform pressure to ensure a tight bond between the two films under heat and pressure. During the lamination process, the uniformity of heating temperature and pressure must be controlled to avoid localized overheating leading to film aging or insufficient pressure causing bubbles. After lamination, an online detection device checks the interlayer bonding to ensure the peel strength meets usage requirements, forming a complete composite film structure that combines barrier and adsorption properties.

[0087] In step S8, after the composite film is formed, post-processing is required to improve stability and meet bag-making requirements. The composite film is sent to a curing chamber and placed at a mild temperature for a sufficient time. The curing process eliminates the internal stress generated during processing, promotes further diffusion and fusion of interlayer molecules, and improves interlayer bonding and overall film smoothness. After curing, the composite film is sent to a slitting machine. According to the design size requirements of the milk tea insulated bag, the film roll is slitted into film sheets of specific specifications using a high-precision slitting device. The cutting accuracy must be controlled during the slitting process to ensure that the edges of the film sheets are neat and burr-free, ultimately obtaining an environmentally friendly finished film that can be directly used to make milk tea insulated bags.

[0088] Comparative Example: Film for regular milk tea insulated bags (control group): Commercially available ordinary PE composite film with an outer PE layer (15μm thick) + an inner PE layer (20μm thick), no adsorption functional layer, and a total thickness of 35μm.

[0089] II. Experimental Procedure

[0090] Simulated milk tea leakage conditions were set up as follows: a 10% sucrose aqueous solution (simulating milk tea sugar content) was prepared, and 5 mL of the solution was dropped into the central area of ​​the two membrane samples (sample size 10 cm × 10 cm, fixed on a horizontal experimental table). The ambient temperature was 25℃ and the relative humidity was 50%.

[0091] Standing and adsorption process: After adding the liquid, let it stand for 10 minutes to allow the liquid to diffuse naturally and come into contact with the membrane layer, avoiding external interference during this period.

[0092] Determination of residual liquid volume: Use a pipette to aspirate the unadsorbed liquid on the surface, weigh and record the residual amount (accurate to 0.01g); then wipe the membrane surface with anhydrous ethanol and measure the mass of residual sugar after wiping (using the anthrone colorimetric method).

[0093] Sensory evaluation of stickiness: Five healthy test subjects (with normal hand skin condition) were selected. After the membrane was left to stand, they directly pressed the surface of the membrane with their index fingers (approximately 5N) for 3 seconds and then slowly lifted it. The stickiness of the hands was scored according to the stickiness (0 points: no stickiness; 1 point: slightly sticky, no visible residue; 2 points: moderately sticky, a small amount of liquid residue is visible; 3 points: severely sticky, liquid is obviously attached). The average score of the five subjects was taken as the final score.

[0094] Repeatability verification: Each sample was tested in triplicate, and the average value was taken as the result.

[0095] III. Evaluation Indicators

[0096] Residual liquid amount (g): directly reflects the adsorption capacity of the membrane for liquid; the lower the value, the better the adsorption effect.

[0097] Surface sugar residue (mg): This reflects the film's ability to capture sugar; the lower the value, the better the anti-sticking effect.

[0098] Stickiness Sensory Rating (points): A direct evaluation of the sticky feeling during use; the lower the score, the better the anti-stickiness experience.

[0099] The specific experimental data are shown in the table below:

[0100]

[0101] Results analysis:

[0102] The experimental group's anti-stick packaging film, through the synergistic effect of diatomaceous earth and modified activated carbon in its internal functional adsorption layer, reduced the residual amount of liquid and sugar in simulated milk tea by 85.3% and 86.5%, respectively, significantly reducing surface free liquid. Simultaneously, the sensory score for stickiness decreased from 2.6 to 0.5, reaching the level of "no obvious stickiness." The control group, lacking adsorption function, had a large amount of liquid and sugar residue remaining on the surface, resulting in severe stickiness. The experiment demonstrates that the anti-stick packaging film effectively solves the stickiness problem of conventional films through a dual mechanism of physical adsorption and chemical capture.

[0103] From the above, we can conclude that:

[0104] In this invention, the inner functional adsorption layer adopts a partitioned design of a core adsorption zone and an auxiliary adsorption zone. The core zone uses linear low-density polyethylene as the substrate, combined with a high proportion of food-grade diatomaceous earth and modified activated carbon. Utilizing the porous structure and microporous adsorption capacity of these materials, it can quickly capture the liquid and sugar generated when milk tea leaks, preventing liquid residue on the membrane surface. The auxiliary adsorption zone enhances the membrane's flexibility with an appropriate amount of thermoplastic elastomer, while simultaneously using a small amount of adsorbent to perform secondary adsorption of dispersed trace amounts of liquid, forming a dual guarantee of "strong core adsorption + auxiliary micro-capture". The outer barrier layer is mainly composed of polyethylene terephthalate, supplemented with linear low-density polyethylene to enhance interlayer bonding. This not only blocks the influence of external moisture and temperature changes on the adsorption effect within the membrane but also maintains the overall structural strength of the membrane material, preventing deformation or damage after liquid adsorption, and fundamentally reducing the sticky feeling when touching the surface.

[0105] In this invention, the environmentally friendly film achieves an anti-sticking function while also ensuring material safety and process stability. All raw materials are food-grade. Adsorbents such as diatomaceous earth and modified activated carbon possess natural environmentally friendly properties, and the linear low-density polyethylene substrate is easy to process and meets food contact standards. It does not release harmful substances during use and can be naturally degraded or recycled after disposal, meeting environmental requirements. In the manufacturing process, raw material pretreatment ensures uniform dispersion of all components, co-extrusion partitioning ensures precise bonding between the core and auxiliary adsorption zones, microgroove structures guide liquid to converge towards the core adsorption zone, and the composite process strengthens the bond between the inner and outer layers. This allows the film to maintain good flexibility and durability while possessing adsorption capabilities, making it suitable for repeated use in milk tea insulated bags while minimizing environmental impact after disposal, thus comprehensively improving the product's user experience and environmental value.

[0106] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "comprising" or any other variations thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An environmentally friendly film for insulated milk tea bags, characterized in that: include: Outer barrier layer and inner functional adsorption layer; The internal functional adsorption layer includes: a core adsorption region and an auxiliary adsorption region; The outer barrier layer includes: Polyethylene terephthalate: as the main substrate, with a mass fraction ranging from 85% to 95%; Linear low-density polyethylene: used as an interlayer bonding component, with a mass fraction ranging from 3% to 7%; Food-grade slip agent: mass fraction range of 1%-3%; Antioxidant: mass fraction range of 0.3% to 0.7%; Food-grade color masterbatch: mass fraction range of 0.3% to 0.7%; The core adsorption region of the internal functional adsorption layer includes: Linear low-density polyethylene: used as the main substrate, with a mass fraction ranging from 70% to 80%; Food-grade diatomaceous earth: as the main adsorbent for capturing sugars with a porous structure, with a mass fraction range of 15% to 22%; Food-grade modified activated carbon: used as an auxiliary adsorbent to enhance the adsorption capacity of micropores, with a mass fraction ranging from 5% to 8%; The auxiliary adsorption region of the internal functional adsorption layer includes: Linear low-density polyethylene: used as the main substrate, with a mass fraction ranging from 85% to 95%; Thermoplastic elastomer: mass fraction range of 3% to 7%; Food-grade diatomaceous earth: mass fraction range of 3% to 6%; Food-grade modified activated carbon: mass fraction range of 1% to 2%.

2. The preparation process of the environmentally friendly film for milk tea insulated bags as described in claim 1, characterized in that: The preparation process includes the following steps: S1: Raw material pretreatment and mixing preparation; First, the polyethylene terephthalate, linear low-density polyethylene, food-grade slip agent, antioxidant, and food-grade color masterbatch required for the outer barrier layer are dried to control the moisture content to be below 0.1%; At the same time, the food-grade diatomaceous earth and modified activated carbon of the inner functional adsorption layer are sieved to ensure uniform particle size distribution, laying the foundation for the subsequent mixing and molding of each layer of materials; S2: Preparation of outer barrier layer substrate; Pretreated polyethylene terephthalate is added to a high-speed mixer at a ratio of 85% to 95% with linear low-density polyethylene, slip agent, antioxidant and color masterbatch, and stirred at 120-140℃ for 20-30 minutes until uniform, and then extruded and cast through a twin-screw extruder to obtain an outer barrier substrate film with a thickness of 15-20μm, for later use; S3: Mixing of core adsorption zone materials; Based on the core adsorption zone formula of the internal functional adsorption layer, linear low-density polyethylene, food-grade diatomaceous earth, and modified activated carbon are added to a mixer in proportion and stirred at 110-130℃ for 30-40 minutes. During this period, ultrasonic dispersion is used to assist in the uniform dispersion of the adsorbent to ensure that there is no agglomeration in the mixed system, which prepares for the subsequent core zone membrane formation. S4: Mixing of auxiliary adsorption zone materials; Simultaneously process the auxiliary adsorption zone materials of the internal functional adsorption layer. Add linear low-density polyethylene, thermoplastic elastomer, food-grade diatomaceous earth, and modified activated carbon to another mixer in proportion. Stir at low speed for 25-35 minutes at 100-120℃. Utilize the compatibilizing effect of thermoplastic elastomer to improve the system compatibility and obtain the auxiliary adsorption zone mixture. S5: Internal functional adsorption layer partition molding; using a co-extrusion die, the core adsorption zone mixture prepared in S3 and the auxiliary adsorption zone mixture prepared in S4 are fed into two independent flow channels of the die respectively. Through the partition control of the die head, the core adsorption zone material is formed in the central area at the bottom of the die, and the auxiliary adsorption zone material is formed in the side and top areas of the die. They are co-extruded and cast into an internal functional adsorption substrate film with a thickness of 20-25μm. S6: Inner layer microgroove structure processing; When the inner functional adsorption substrate film obtained in S5 is cooled to 60-70℃, it is sent into the molding equipment and molded through the preset radial groove template to form a flow guiding groove on the surface of the inner layer film, which converges from the edge of the bag opening and the middle of the side to the bottom center. After the processing is completed, it is naturally cooled to room temperature to enhance the subsequent liquid flow guiding effect. S7: Inner and outer layer composite molding; The outer barrier substrate film prepared in S2 is aligned with the inner functional adsorption substrate film treated in S6, and fed into the composite machine. The two films are then laminated into one by hot pressing, ensuring that the composite strength reaches more than 2.5N / 15mm, forming a complete environmentally friendly film substrate. S8: Post-processing and slitting; The composite film obtained in S7 is cured to eliminate internal stress and improve interlayer bonding. Then, according to the size requirements of the milk tea insulated bag, it is slitting into film sheets of specific specifications by a slitting machine, and finally an environmentally friendly film product that can be used to make milk tea insulated bags is obtained.

3. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S1, the polyethylene terephthalate, linear low-density polyethylene, food-grade slip agent, antioxidant, and food-grade masterbatch required for the outer barrier layer are first dried. Residual moisture in the materials is removed using a hot air circulating drying device, and the moisture content is controlled to a low level to avoid bubbles or pinholes caused by moisture evaporation during subsequent processing. The food-grade diatomaceous earth and modified activated carbon of the inner functional adsorption layer are mechanically sieved. Particles with uniform particle size distribution are separated through multiple layers of sieves to remove large impurities and ultrafine dust, ensuring that the adsorbent can be uniformly dispersed in the subsequent mixing process, laying the foundation for the molding quality of each layer of materials.

4. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S2, the preparation of the outer barrier layer substrate requires strict control of mixing and extrusion parameters to ensure the mechanical properties and barrier properties of the film. The dried polyethylene terephthalate is added to a high-speed mixer along with linear low-density polyethylene, slip agent, antioxidant, and masterbatch in the main proportion. The mixer speed is set to 800-1000 rpm, heated to 125-135 degrees Celsius, and continuously stirred for 25-30 minutes to ensure complete melting and dispersion of all components. After mixing, the material is fed into a twin-screw extruder at a rate of 20-25 kg / h via a feeder. The temperatures of each zone of the extruder are controlled sequentially as follows: Zone 1: 170-180 degrees Celsius; Zone 2: 185-195 degrees Celsius; Zone 3: 200-210 degrees Celsius; Die head temperature: 205-215 degrees Celsius. The screw speed is adjusted to 150-180 rpm, further homogenizing the material through the shearing and conveying action of the screw.

5. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S3, during mixing, the equipment temperature is controlled to the range where the substrate begins to melt, the stirring device is started to slowly fuse the materials, and the ultrasonic dispersion auxiliary system is turned on to break up the agglomeration between adsorbent particles using high-frequency vibration, ensuring that diatomaceous earth and modified activated carbon are uniformly dispersed in the polyethylene substrate. The entire mixing process needs to last for a sufficient time until sampling and observation confirm that there is no obvious agglomeration of adsorbent, forming a uniformly dispersed mixed system, which provides a guarantee for the subsequent formation of the core area membrane and the adsorption performance.

6. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S4, while the materials in the core adsorption zone are being mixed, another set of mixing equipment is started to process the materials in the auxiliary adsorption zone. Linear low-density polyethylene is used as the main substrate, and thermoplastic elastomer, food-grade diatomaceous earth and modified activated carbon are added in proportion. The equipment temperature is controlled to a range where the thermoplastic elastomer softens but does not decompose. A low stirring speed is used for mixing to avoid high-speed shearing that could cause the elastomer molecular chains to break.

7. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S5, the core adsorption zone mixture and the auxiliary adsorption zone mixture are fed into two independent channels of the co-extrusion die. The temperature of the core adsorption zone channel is set to 160-170 degrees Celsius, and the temperature of the auxiliary adsorption zone channel is set to 155-165 degrees Celsius. The overall temperature of the die head is controlled at 165-175 degrees Celsius. The material flow ratio between the core zone and the auxiliary zone is adjusted to 1:4 through the channel distribution system to ensure that the core adsorption zone accounts for 20% of the inner film area and the auxiliary adsorption zone accounts for 80% after molding. After the molten material is extruded through the die head, it enters the casting cooling roller at a speed of 0.8-1.2 meters per minute. The temperature of the cooling roller is controlled at 30-40 degrees Celsius, and the cooling time is 15-20 seconds to quickly solidify the film layer. The total thickness of the molded internal functional adsorption substrate film is controlled at 20-25 micrometers, with the core adsorption zone thickness slightly higher than the auxiliary adsorption zone to ensure a balance between adsorbent content and structural stability.

8. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S6, after the internal functional adsorption substrate film is formed, the inner layer microgroove structure is immediately processed. The film layer cooled to a certain temperature is sent into the molding equipment. At this time, the film layer needs to be kept in an appropriate softened state to ensure that a clear groove structure can be imprinted by the template. The template surface in the molding equipment is provided with a preset radial groove pattern. By applying uniform pressure, the template is made to be in close contact with the film surface, and a guide groove converging from the edge to the bottom center is imprinted on the film surface.

9. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S7, the inner and outer layer composite forming is a key step that determines the overall performance of the environmentally friendly membrane. It is necessary to control the interlayer bonding force and membrane surface quality through hot pressing parameters. After aligning the outer barrier substrate membrane and the inner functional adsorption substrate membrane, they are fed into the laminating machine. The temperature of the hot pressing roller of the laminating machine is set to 135-145 degrees Celsius, the pressure is adjusted to 0.35-0.45 MPa, and the lamination speed is controlled at 1.5-2 meters per minute to ensure that the two membranes are fully fused under the action of hot pressing.

10. The environmentally friendly film for milk tea insulated bags and its preparation process as described in claim 1, characterized in that: In step S8, after the composite film is formed, it needs to be post-processed to improve stability and meet the requirements of bag making. The composite film is sent to the curing chamber and placed at a mild temperature for a sufficient time. The curing process eliminates the internal stress generated during processing, promotes further diffusion and fusion of interlayer molecules, and improves the interlayer bonding force and overall flatness of the film layer. After curing, the composite film is sent to the slitting machine. According to the design size requirements of the milk tea insulated bag, the film roll is slitted into film sheets of specific specifications by a high-precision slitting device. The cutting accuracy needs to be controlled during the slitting process to ensure that the edges of the film sheets are neat and burr-free. Finally, an environmentally friendly film product that can be directly used to make milk tea insulated bags is obtained.

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