Aluminum-plastic composite sealing film and preparation method thereof

Abstract

This invention discloses an aluminum-plastic composite sealing film and its preparation method. The aluminum-plastic composite sealing film comprises, from top to bottom, a high-temperature resistant coating, an aluminum foil, a composite adhesive layer, a PET film, another composite adhesive layer, and a PP film. The preparation method includes: pre-compositing the PET film and PP film into a PET / PP pre-composite film; after the aluminum foil is unwound once, the upper surface is coated with a high-temperature resistant coating and flash-dried to form a semi-dry film state, and the lower surface is coated with composite adhesive and laminated with the PET / PP pre-composite film, so that the PET side is in contact with the composite adhesive; a single heating and drying process simultaneously cures the high-temperature resistant coating and the composite adhesive, followed by cooling and winding. The aluminum foil is unwound only once, eliminating mechanical damage caused by multiple tractions; the flash-dried semi-dry film balances the solvent evaporation rate on both sides, and the coatings on both sides are successfully cured in one drying process, resulting in symmetrical thermal stress and suppressed warping deformation; the temperature does not exceed 180℃, suppressing grain growth and maintaining excellent tensile strength and elongation; intermediate cooling is eliminated, shortening the production line and reducing equipment investment and energy consumption.

Description

Technical Field

[0001] This invention relates to the field of aluminum foil technology, specifically to an aluminum-plastic composite sealing film and its preparation method. Background Technology

[0002] Easy-tear lids are widely used for sealing the tops of food packaging containers such as milk powder cans, coffee cans, and luncheon meat cans. They are made by stamping tinplate cap rings and aluminum foil film. Canned foods usually need to be cooked before processing and consumption, so the aluminum foil of easy-tear lids must have excellent resistance to cooking, meaning that it must maintain its seal without deterioration, the coating must not crack or peel off, and the aluminum foil must not react with the contents under high-temperature steam.

[0003] Chinese Patent CN109051184B, filed in 2018, discloses an easy-tear lid with a retort-resistant aluminum foil. The aluminum foil includes an aluminum foil body, and, from the inside out, a color layer and a protective layer on one side of the aluminum foil body, and, from the inside out, a composite adhesive layer one, a nylon film layer, a composite adhesive layer two, and a PP film layer on the other side of the aluminum foil body. This retort-resistant aluminum foil enhances its overall strength through the nylon film layer and achieves heat-sealing adhesion to tinplate through the PP film layer. After being retorted at 121°C, the product does not crack, fade, or leak air.

[0004] However, the existing manufacturing process described above suffers from significant redundancy. According to the patent specification, the aluminum foil preparation involves the following steps: first, a protective layer is coated onto one side of the aluminum foil and heated and dried for 3-5 days; then, a composite adhesive layer is coated onto the other side of the aluminum foil and heated and dried, then laminated with a nylon film and cured for another 3-5 days; finally, a second composite adhesive layer is coated onto the other side of the nylon film and heated and dried, then laminated with a PP film and cured for another 3-5 days. In this process, the aluminum foil undergoes three unwinding processes, three coating processes, three heating and drying processes, and three curing processes, resulting in a lengthy process chain, a large production line footprint, and high equipment investment and energy consumption.

[0005] More importantly, aluminum foil itself is only 0.02-0.08mm thick, making it soft and easily deformable. Repeatedly subjected to traction tension during multiple unwinding and rewinding processes, it is highly susceptible to scratches, wrinkles, and even breakage. This leads to a decline in the mechanical properties of the aluminum foil, impairing its tensile strength and elongation, ultimately affecting the stamping yield of the easy-tear cap and the sealing reliability after cooking. Furthermore, repeated heating and drying prolongs the cumulative heating time of the aluminum foil, exacerbating the tendency for grain growth and further deteriorating its mechanical properties. Multiple curing cycles also significantly lengthen the production cycle and reduce production efficiency.

[0006] Therefore, how to reduce the number of times aluminum foil is unwound and rewound while ensuring its resistance to boiling and cooking, shorten the production process, and reduce mechanical and thermal damage to aluminum foil during the preparation process has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] In order to overcome the above-mentioned defects of the prior art, the present invention provides an aluminum-plastic composite sealing film and its preparation method to solve at least some of the technical problems mentioned in the background art.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an aluminum-plastic composite sealing film, wherein the aluminum-plastic composite sealing film comprises, from top to bottom, a high-temperature resistant coating, an aluminum foil, a composite adhesive layer, a PET film, another composite adhesive layer, and a PP film; characterized in that the preparation method includes the following steps: The PET film and PP film are pre-composite to form a PET / PP pre-composite film; Aluminum foil unwinding; A high-temperature resistant coating is applied to the upper surface of the aluminum foil to form a high-temperature resistant coating. The high-temperature resistant coating is flash-baked using infrared radiation heating with a radiation wavelength of 2-4μm, a radiation intensity of 50-80kW / m², and a flash-baking time of 1-3 seconds. After flash-baking, the surface temperature of the high-temperature resistant coating is 80-100℃ and the surface is in a semi-dry film state. A composite adhesive is applied to the lower surface of the aluminum foil, and the PET / PP pre-composite film is laminated onto the composite adhesive, so that the PET side is in contact with the composite adhesive; The aluminum foil is subjected to a single heating and drying process to simultaneously cure the high-temperature resistant coating and the composite adhesive. The temperature of the single heating and drying process does not exceed 180°C. The dried aluminum foil is cooled and then wound up.

[0009] Optionally, the specific steps for pre-compositing the PET film and the PP film to form a PET / PP pre-composite film are as follows: coating a composite adhesive on one side of the PET film to form a first composite adhesive layer; laminating the PP film onto the first composite adhesive layer so that the PP film is in contact with the first composite adhesive layer; heating and drying the PET film and the PP film to cure the first composite adhesive layer and form the PET / PP pre-composite film.

[0010] Optionally, the PET film has a thickness of 0.015 mm, and the PP film has a thickness of 0.035 mm; the PET film is subjected to double-sided corona treatment before pre-lamination, and the corona value is not less than 38 dynes; the coating amount of the first composite adhesive is 2-4 g / m²; the heating and drying temperature is 80-120℃, and the drying time is 5-10 seconds.

[0011] Optionally, the primary heating and drying adopts a gradient temperature increase method, which includes a low-temperature volatilization zone, a medium-temperature curing zone, and a high-temperature setting zone in sequence. The temperature of the low-temperature volatilization zone is 60-80℃, the temperature of the medium-temperature curing zone is 100-130℃, and the temperature of the high-temperature setting zone is 150-180℃.

[0012] Optionally, the duration of the low-temperature evaporation zone is 40%-50% of the total duration of the single heating and drying, the duration of the medium-temperature curing zone is 30%-40% of the total duration of the single heating and drying, and the duration of the high-temperature setting zone is 10%-20% of the total duration of the single heating and drying.

[0013] Optionally, during the primary heating and drying process, a blowing device is provided on one side of the upper surface of the aluminum foil, the blowing device blowing air at a temperature of 40-60℃ and a wind speed of 5-8m / s; a suction device is provided on one side of the lower surface of the aluminum foil, the suction device having a wind speed of 3-5m / s.

[0014] Optionally, the high-temperature resistant coating includes a two-component varnish, which includes an acrylic resin and a curing agent, and the composite adhesive includes an acrylic resin and a solvent. The acrylic resin in the high-temperature resistant coating has a molecular weight of 5,000-15,000, and the acrylic resin in the composite adhesive has a molecular weight of 20,000-50,000.

[0015] Optionally, the acrylic resin in the high-temperature resistant coating has hydroxyl and carboxyl functional groups, and the acrylic resin in the composite adhesive has epoxy and amino functional groups. The high-temperature resistant coating in the semi-dry film state and the composite adhesive undergo a condensation reaction in the high-temperature setting zone to form a chemical bond.

[0016] Optionally, the flash drying uses far-infrared radiation heating, the wavelength of the far-infrared radiation is 3-4μm, the radiation intensity is 60-70kW / m², the flash drying time is 1.5-2.5 seconds, and the surface temperature of the high-temperature resistant coating after flash drying is 85-95℃.

[0017] A second aspect of the present invention provides an aluminum-plastic composite sealing film, wherein the aluminum-plastic composite sealing film is prepared by the above-described method for preparing aluminum-plastic composite sealing film.

[0018] The specific effects of this invention are as follows: Pre-compositing PET and PP films into a PET / PP pre-composite film is an independent step in the aluminum foil processing, allowing for batch production before the aluminum foil is loaded onto the machine. The aluminum foil is unwound only once, compared to the prior art where aluminum foil requires three unwinding cycles, eliminating the risk of scratches, wrinkles, and breakage caused by repeated traction tension. The aluminum foil is only 0.02-0.08 mm thick, with a soft material and limited extensibility. Multiple unwinding cycles lead to accumulated lattice slip on the aluminum foil surface, resulting in decreased tensile strength and deteriorated elongation. Single unwinding minimizes mechanical damage and maintains excellent mechanical properties.

[0019] A high-temperature resistant coating is formed by coating the surface of aluminum foil, which provides the foundation for subsequent resistance to boiling. The high-temperature resistant coating is then flash-dried using infrared radiation heating. The radiation wavelength of 2-4 μm falls within the characteristic absorption band of organic coating molecules, allowing energy to be directly absorbed by the surface molecules, resulting in high heating efficiency. The radiation intensity of 50-80 kW / m² is matched with the flash-driing time of 1-3 seconds, enabling rapid removal of surface solvents within seconds. After flash-driing, the surface temperature is 80-100℃ and the coating is in a semi-dry film state. This temperature is higher than the boiling point of commonly used solvents such as ethyl acetate (77℃), providing sufficient kinetics for solvent removal, but lower than the glass transition temperature of acrylic resin, meaning the resin is not fully cured and the coating retains flexibility. This semi-dry film state lays the foundation for primary heat drying: the surface already possesses mechanical strength and will not drip or bubble due to subsequent drying airflow disturbances; solvent channels are still preserved internally, significantly reducing the solvent evaporation load, which kinetically matches the initial drying behavior of the underlying composite adhesive. The aluminum foil undergoes a single heat-drying process to simultaneously cure the high-temperature resistant coating and the composite adhesive, with the temperature not exceeding 180℃. The key to successful single-drying lies in the introduction of a flash-baked semi-dry film state: after flash drying, a significant amount of solvent is removed from the surface of the high-temperature resistant coating, reducing the difference in solvent evaporation rates between the coating and the composite adhesive during the single-drying process. This allows for a unified temperature profile that balances both sides. The thermal resistance of the semi-dry film slows down the internal heating rate of the high-temperature resistant coating, synchronizing it with the heating rate of the composite adhesive side. This ensures symmetrical thermal stress on both sides of the aluminum foil, suppressing warping and deformation. By keeping the temperature below 180℃, the cumulative heating time of the aluminum foil is shortened due to the combined process, inhibiting grain growth and maintaining excellent tensile strength and elongation.

[0020] The dried aluminum foil is cooled and rolled up, requiring only a single cooling operation, eliminating the intermediate cooling between two drying cycles in existing technologies. This shortens the production line length and reduces equipment investment and energy consumption. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of a method for preparing an aluminum-plastic composite sealing film according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In existing technologies, the coatings on both sides of the aluminum foil need to be dried independently. This is because if both coatings are placed in the same drying oven simultaneously, the solvents on both sides will evaporate at the same time. The solvent on the upper surface of the aluminum foil will diffuse upwards, and the solvent on the lower surface will diffuse downwards, creating a concentration gradient of solvent vapor on both sides of the aluminum foil. If the ventilation design is inadequate, the solvent vapors on both sides may penetrate each other or accumulate locally, resulting in uneven drying. More importantly, the coating thickness, solvent content, and resin system on both sides are usually different. If dried simultaneously, one side of the coating may be over-cured while the other side is not yet fully cross-linked, making it difficult to find a uniform temperature profile that takes both sides into account. Therefore, existing technologies are forced to use two independent drying processes, treating only one side at a time, with the cured coating on the other side serving as a stable substrate. However, this results in the aluminum foil being subjected to two asymmetric thermal stresses. The coating on the side that is dried first shrinks and sets, while the undried side remains in a swollen state, causing the aluminum foil to curl and warp towards the side that was dried first, and the cumulative heating time is prolonged.

[0024] Therefore, as Figure 1 As shown, the first aspect of the present invention provides a method for preparing an aluminum-plastic composite sealing film. The aluminum-plastic composite sealing film comprises, from top to bottom, a high-temperature resistant coating, an aluminum foil, a composite adhesive layer, a PET film, another composite adhesive layer, and a PP film. The preparation method includes the following steps: Pre-laminating PET and PP films into PET / PP pre-composite films is a separate step from the aluminum foil processing, allowing for batch production before the aluminum foil is loaded onto the machine. The aluminum foil undergoes only one unwinding process, compared to the three unwinding processes required in existing technologies. This eliminates the risk of scratches, wrinkles, and breakage caused by repeated traction tension. Aluminum foil is only 0.02-0.08mm thick, with a soft material and limited ductility. Multiple unwinding processes lead to accumulated lattice slip on the aluminum foil surface, resulting in decreased tensile strength and deteriorated elongation. Single unwinding minimizes mechanical damage and maintains excellent mechanical properties.

[0025] Unwind the aluminum foil.

[0026] A high-temperature resistant coating is applied to the upper surface of the aluminum foil to form a high-temperature resistant coating; this coating provides the basis for subsequent resistance to boiling.

[0027] The high-temperature resistant coating is flash-baked using infrared radiation heating with a wavelength of 2-4 μm, a radiation intensity of 50-80 kW / m², and a flash-baking time of 1-3 seconds. After flash-baking, the surface temperature of the high-temperature resistant coating is 80-100℃, and the surface is in a semi-dry film state. The high-temperature resistant coating is flash-baked using infrared radiation heating with a wavelength of 2-4 μm, which is in the characteristic absorption band of organic coating molecules. The energy is directly absorbed by the surface molecules, resulting in high heating efficiency. The radiation intensity of 50-80 kW / m² is matched with the flash-baking time of 1-3 seconds, which allows the surface solvent to be rapidly removed within a few seconds. After flash-baking, the surface temperature is 80-100℃, and the surface is in a semi-dry film state. This temperature is higher than the boiling point of commonly used solvents such as ethyl acetate (77℃), providing sufficient impetus for the removal of surface solvent, but it is lower than the glass transition temperature of acrylic resin. The resin is not completely cured, and the coating still has flexibility. The semi-dry film state lays the foundation for the first heat drying: the surface layer already possesses mechanical strength and shape retention, preventing sagging or bubbling due to airflow disturbances during subsequent drying; the interior still retains solvent channels, allowing internal solvents to continue migrating and evaporating along the formed micropores to the surface in the low-temperature evaporation zone of the first drying. This means that by the time it enters the first drying oven, the solvent evaporation of the high-temperature resistant coating has been significantly reduced, and its drying behavior has changed from "rapid removal of large amounts of solvent" to "slow migration of residual solvent," kinetically matching the initial drying behavior of the composite adhesive. The composite adhesive is fully wet when coated on the lower surface of the aluminum foil, with the highest solvent content, undergoing a solvent removal process similar to that after flash drying of the high-temperature resistant coating in the low-temperature evaporation zone of the first drying; since most of the solvent has been pre-removed from the high-temperature resistant coating, the difference in solvent evaporation rates between the two coatings in each temperature zone of the first drying is reduced, and a unified temperature curve can simultaneously consider both sides.

[0028] A composite adhesive is applied to the lower surface of the aluminum foil, and a PET / PP pre-composite film is laminated onto the composite adhesive, so that the PET side is in contact with the composite adhesive.

[0029] The aluminum foil undergoes a single heat-drying process to simultaneously cure the high-temperature resistant coating and the composite adhesive. The temperature during this single heat-drying process does not exceed 180℃. The key to successful single-stage drying lies in the introduction of a flash-baked semi-dry film state: after flash-baking, a significant amount of solvent is removed from the surface of the high-temperature resistant coating, reducing the difference in solvent evaporation rates between the coating and the composite adhesive during the single-stage drying process. This allows for a unified temperature profile that balances both sides. The thermal resistance of the semi-dry film slows down the internal heating rate of the high-temperature resistant coating, synchronizing it with the heating rate of the composite adhesive side. This ensures symmetrical thermal stress on both sides of the aluminum foil, suppressing warping and deformation. By keeping the temperature below 180℃, the cumulative heating time of the aluminum foil is shortened due to the combined process, inhibiting grain growth and maintaining excellent tensile strength and elongation.

[0030] The dried aluminum foil is cooled and rolled up, requiring only a single cooling operation, eliminating the intermediate cooling between two drying cycles in existing technologies. This shortens the production line length and reduces equipment investment and energy consumption.

[0031] As an optional implementation method, the specific steps for pre-laminating PET and PP films to form a PET / PP pre-composite film are as follows: A composite adhesive is coated on one side of the PET film to form a first composite adhesive layer; the PP film is then laminated onto the first composite adhesive layer, bringing the PP film into contact with the first composite adhesive layer; the PET and PP films are heated and dried to cure the first composite adhesive layer, forming the PET / PP pre-composite film. If the PET and PP films are laminated separately on the aluminum foil production line, the aluminum foil must first be laminated with the PET film, dried, and cured, then laminated with the PP film, dried, and cured again, adding at least two unwinding and two drying cycles to the aluminum foil. However, by pre-laminating the PET and PP films, the aluminum foil only needs to be laminated once with the PET / PP pre-composite film as a whole, reducing the number of unwinding and drying cycles. Furthermore, the pre-lamination of PET and PP films can be performed on dedicated lamination equipment. This equipment does not need to accommodate the thin material characteristics of aluminum foil, allowing for higher lamination pressure and faster material feeding speeds, resulting in stable lamination quality and higher production efficiency than layer-by-layer lamination on the aluminum foil production line. After the first composite adhesive layer is cured, it forms a stable interlayer bond. The peel strength between the PET film and the PP film remains reliable during the subsequent aluminum foil processing and cooking process, and will not soften or delaminate again due to the temperature conduction during the first drying of the aluminum foil.

[0032] As an optional implementation, the PET film has a thickness of 0.015 mm, and the PP film has a thickness of 0.035 mm. The PET film undergoes double-sided corona treatment before pre-lamination, with a corona value of not less than 38 dynes. The coating amount of the first composite adhesive is 2-4 g / m². The heating and drying temperature is 80-120℃, and the drying time is 5-10 seconds. The 0.015 mm PET film thickness and 0.035 mm PP film thickness provide a thin barrier layer that adheres tightly to the aluminum foil, effectively blocking oxygen and water vapor penetration. The thick PP film provides sufficient heat-sealing area and adhesion strength to the tinplate. Before pre-lamination, the PET film undergoes double-sided corona treatment with a corona value of no less than 38 dynes. The corona treatment breaks the molecular chains on the PET film surface and introduces polar groups, increasing surface tension and thus enhancing the wettability and adhesion to the first composite adhesive layer and subsequent composite adhesive layers with the aluminum foil side. Double-sided corona treatment ensures that both sides of the PET film have highly active surfaces; one side is pre-laminated with the PP film, and the other side is laminated with the aluminum foil, resulting in balanced bonding strength and preventing interlayer delamination. The coating amount of the first composite adhesive is 2-4 g / m². This coating amount ensures sufficient adhesion between the PET and PP films while avoiding excessively thick adhesive layers that could lead to excessive solvent residue or embrittlement after drying. If the coating amount is less than 2 g / m², the adhesive layer coverage will be incomplete, easily causing bubbles or localized delamination. If it is greater than 4 g / m², the solvent evaporation path during drying will be too long, and surface curing will seal the internal solvent channels, forming pinholes or bubbles. The heating and drying temperature is 80-120℃ and the time is 5-10 seconds. This parameter window is lower than the heat distortion temperature of PP film (about 120-150℃), which avoids the PP film from softening and deforming during the pre-composite process. At the same time, the temperature is higher than the boiling point of commonly used solvents (such as ethyl acetate at 77℃), which ensures that the solvent evaporates fully. The drying time of 5-10 seconds is matched with the coating amount of 2-4g / m², which achieves rapid curing without damaging the film material.

[0033] As an optional implementation, the single-stage heating and drying process employs a gradient temperature increase method, sequentially including a low-temperature evaporation zone, a medium-temperature curing zone, and a high-temperature setting zone. The low-temperature evaporation zone has a temperature of 60-80℃, the medium-temperature curing zone has a temperature of 100-130℃, and the high-temperature setting zone has a temperature of 150-180℃. Through the gradient connection of these three temperature zones, the solvents in the high-temperature resistant coating and composite adhesive evaporate in stages in an orderly manner, and the resin cross-links gradually in stages, ultimately achieving uniform curing of the coating without defects. Specifically, both the high-temperature resistant coating and the composite adhesive contain solvents. If directly placed in the high-temperature zone, the solvents will boil violently, generating vapor bubbles that break through the surface resin, forming pinholes. If kept in the low-temperature zone for a prolonged period, the solvents will evaporate slowly, resulting in low production efficiency and insufficient resin pre-crosslinking. The low-temperature evaporation zone (60-80℃) allows the solvent to migrate and evaporate from the interior of the coating to the surface. This temperature is higher than the boiling point of commonly used solvents such as ethyl acetate, providing sufficient evaporation momentum, but lower than the glass transition temperature of the resin. The resin is not yet cross-linked, the coating remains fluid, and the solvent channels are open. The medium-temperature curing zone (100-130℃) initiates the cross-linking reaction of the resin molecular chains, and the coating gradually transforms from a liquid to a solid state. At this point, most of the solvent has been removed, and a small amount of residual solvent from the cross-linking network formation process can still escape along the micropores. The high-temperature setting zone (150-180℃) ensures complete cross-linking and densification of the resin, resulting in a smooth coating surface with excellent gloss. The temperature does not exceed 180℃ to prevent excessive growth of aluminum foil grains. These three temperature zones are sequentially connected, matching the solvent evaporation rate with the resin cross-linking rate, resulting in uniform, bubble-free curing of the coating and a smooth, pinhole-free surface.

[0034] As an optional implementation, the duration of the low-temperature evaporation zone is 40%-50% of the total heating and drying time, the duration of the medium-temperature curing zone is 30%-40% of the total heating and drying time, and the duration of the high-temperature setting zone is 10%-20% of the total heating and drying time. The low-temperature evaporation zone, accounting for 40%-50%, provides sufficient time for solvent migration and evaporation. If this percentage is too short (e.g., below 40%), the solvent will not be fully removed before entering the medium-temperature zone, causing premature cross-linking of the resin and sealing of the solvent channels, resulting in solvent vapor accumulation and the formation of bubbles within the coating. If this percentage is too long (e.g., above 50%), excessive pre-crosslinking of the resin leads to insufficient fluidity during subsequent high-temperature setting, resulting in poor surface gloss of the coating. The medium-temperature curing zone, accounting for 30%-40%, allows the resin to gradually crosslink after most of the solvent has been removed. This duration matches the resin reaction kinetics, ensuring a moderate degree of crosslinking. This avoids both insufficient crosslinking leading to low cohesive strength and excessive crosslinking leading to coating embrittlement. The high-temperature setting zone accounts for 10%-20% of the total area. This zone completes the final densification process after the resin has largely cross-linked, requiring a relatively short setting time. If this zone is too long, the cumulative heating time of the aluminum foil will be prolonged, increasing the risk of grain growth. This time allocation ensures uniform curing of the coating on both sides, symmetrical thermal stress across the aluminum foil, and avoids curling and deformation caused by a hardened surface layer and a soft inner layer. The final coating exhibits excellent smoothness and gloss.

[0035] As an optional implementation, during the single-stage heating and drying process, a blowing device is installed on one side of the upper surface of the aluminum foil, blowing air at a temperature of 40-60℃ with a wind speed of 5-8 m / s; a suction device is installed on one side of the lower surface of the aluminum foil, with a wind speed of 3-5 m / s. This differentiated ventilation design on both sides allows for the directional discharge of the high-temperature resistant coating solvent and the composite adhesive solvent, avoiding cross-interference of solvent vapors and improving drying efficiency. Specifically, the high-temperature resistant coating is located on the upper surface of the aluminum foil. After its solvent evaporates, it diffuses upwards. The blowing device delivers air at 40-60℃, a temperature lower than the temperature of the medium-temperature curing zone, which will not interfere with the thermal field distribution inside the oven, but higher than the ambient temperature, accelerating the upward dispersion of solvent vapors. The wind speed of 5-8 m / s forms a stable laminar flow, promptly carrying the solvent vapor away from the aluminum foil surface, reducing the surface solvent partial pressure, and promoting the migration of solvent from the coating interior to the surface. The composite adhesive is located on the lower surface of the aluminum foil. After its solvent evaporates, it diffuses downwards. The suction device, with a wind speed of 3-5 m / s, creates negative pressure to draw the composite adhesive solvent downwards. The wind speed is lower than the blowing speed on the upper surface to avoid excessive negative pressure causing the PET / PP pre-composite film to vibrate or shift on the lower surface of the aluminum foil, affecting the flatness of the composite. The solvent discharge paths on both sides do not interfere with each other. The solvent on the upper surface is blown upwards, while the solvent on the lower surface is drawn downwards. The two coatings dry simultaneously and thoroughly, further shortening the drying time. Moreover, the heat flux density on both sides of the aluminum foil tends to be balanced, resulting in better thermal stress symmetry.

[0036] As an optional implementation, the high-temperature resistant coating includes a two-component varnish comprising acrylic resin and a curing agent, and a composite adhesive comprising acrylic resin and a solvent. The acrylic resin in the high-temperature resistant coating has a molecular weight of 5000-15000, and the acrylic resin in the composite adhesive has a molecular weight of 20000-50000. The high-temperature resistant coating is a thin layer (coating weight 1.0-2.0 g / m²), and needs to possess both density and flexibility. Low molecular weight acrylic resin (5000-15000) has low solution viscosity, making it easy to coat into a thin and uniform coating. Furthermore, its short molecular chains and high cross-linking density result in a dense coating with excellent barrier properties after curing. If the molecular weight is too high, the solution viscosity is high, and uneven thickness or poor leveling is likely to occur during thin-layer coating. The composite adhesive serves as the bonding layer (coating weight 3-6 g / m²), requiring both cohesive strength and initial tack. High molecular weight acrylic resins (20,000-50,000) have long molecular chains and high entanglement, resulting in a tough and strong peel layer after curing. Conversely, if the molecular weight is too low, the cohesive strength of the adhesive layer is insufficient, leading to adhesion failure with PET film and aluminum foil. The difference in molecular weight between the two resins optimizes the functions of both the high-temperature coating and the composite adhesive. The thin, flexible, and dense high-temperature coating provides a strong and durable bond, while the thick, robust composite adhesive offers superior adhesion. During the initial drying process, the low molecular weight resin cross-links rapidly in the high-temperature setting zone, forming a dense network first. The high molecular weight resin then gradually entangles and cross-links. Both resins cure simultaneously within their respective temperature windows without interference, resulting in a strong interlayer bond and full utilization of their respective properties.

[0037] As an optional implementation, the acrylic resin in the high-temperature resistant coating has hydroxyl and carboxyl functional groups, while the acrylic resin in the composite adhesive has epoxy and amino functional groups. In the semi-dry film state, the high-temperature resistant coating and the composite adhesive undergo a condensation reaction in the high-temperature setting zone, forming chemical bonds. Through the chemical reaction between functional groups, a covalent bond interface is formed between the high-temperature resistant coating and the composite adhesive, replacing simple physical adsorption or intermolecular forces and significantly improving the interlayer bonding strength. Specifically: In the semi-dry film state, the surface resin of the high-temperature resistant coating has been initially cross-linked but still retains active functional groups (hydroxyl and carboxyl groups). After the composite adhesive is applied, its solvent is miscible with the residual solvent on the surface of the high-temperature resistant coating. The high molecular weight resin in the composite adhesive penetrates into the surface of the high-temperature resistant coating, while the low molecular weight resin in the high-temperature resistant coating diffuses into the bottom layer of the composite adhesive, forming an interpenetrating transition layer. Upon entering the high-temperature setting zone, the hydroxyl and carboxyl groups in the high-temperature resistant coating undergo a condensation reaction with the epoxy and amino groups in the composite adhesive. The hydroxyl and epoxy groups undergo ring-opening addition, and the carboxyl and amino groups undergo amidation, forming covalent bonds such as ether bonds, ester bonds, and amide bonds. The bond energy of this chemical bond (typically 200-400 kJ / mol) is much higher than that of hydrogen bonds or van der Waals forces (typically 10-40 kJ / mol), increasing the interfacial bonding strength between the high-temperature resistant coating and the composite adhesive by an order of magnitude. During the subsequent 75-minute steam boiling at 119°C, the covalently bonded interface does not hydrolyze or degrade due to the humid and hot environment, the high-temperature resistant coating does not separate from the aluminum foil, the composite adhesive layer remains intact and does not degrade, and the steam resistance of the aluminum foil is fundamentally guaranteed.

[0038] As an optional implementation method, flash drying utilizes far-infrared radiation heating. The wavelength of far-infrared radiation is 3-4 μm, the radiation intensity is 60-70 kW / m², and the flash drying time is 1.5-2.5 seconds. After flash drying, the surface temperature of the high-temperature resistant coating is 85-95℃. The far-infrared radiation wavelength of 3-4 μm is within the characteristic absorption band of organic coating molecules. The radiation energy is directly absorbed by the resin and solvent molecules in the coating, resulting in high heating efficiency and moderate penetration depth, primarily acting on the coating surface. The radiation intensity of 60-70 kW / m² is in the mid-to-high range of 50-80 kW / m², ensuring sufficient energy input per unit time, allowing the surface solvent to evaporate rapidly within 1.5-2.5 seconds. The flash drying time of 1.5-2.5 seconds balances efficiency and controllability. If the time is too short, the solvent removal will be insufficient, resulting in an unstable semi-dry film state that is easily dissolved or damaged when in contact with the composite adhesive later. If the time is too long, the surface layer will be over-cured, leaving too little solvent residue inside, making the coating cross-linking behavior uncontrollable during subsequent primary drying. The surface temperature of 85-95℃ is approximately 8-18℃ higher than the boiling point of ethyl acetate (77℃), providing sufficient impetus for solvent removal and initial cross-linking and shaping of the surface resin. Simultaneously, this temperature is lower than the glass transition temperature of acrylic resin (typically 100-120℃), meaning the resin is not fully cured, and the coating remains flexible. It is not sticky to the touch, but a light scratch with a fingernail will leave a mark. This state provides a quantifiable characteristic of the semi-dry film. Within this parameter window, the semi-dry film exhibits optimal stability, allowing for controllable coating curing behavior during subsequent drying. The coating will not drip due to gravity or tension during aluminum foil transport, nor will it be excessively dissolved upon contact with the composite adhesive.

[0039] The core mechanism by which this application achieves successful single-stage heating and drying lies in the introduction of a flash-dried semi-dry film state and the synergistic design of the resin systems for coating on both sides.

[0040] First, flash drying allows the high-temperature resistant coating to enter a controllable semi-cured state beforehand, reducing the solvent evaporation load during the first drying stage. After flash drying, the surface temperature of the high-temperature resistant coating reaches 80-100℃, and more than 80% of the surface solvent has been removed. The resin has initially cross-linked to form a film, but 40%-50% of the solvent remains inside. At this point, the coating is in a "semi-dry film state"—the surface has mechanical strength and shape retention, and will not drip or bubble due to airflow disturbances during the subsequent first drying stage; the interior still retains solvent channels, and in the low-temperature evaporation zone of the first drying stage, the internal solvent can continue to migrate and evaporate to the surface along the formed micropores. This means that when entering the first drying oven, the solvent evaporation of the high-temperature resistant coating has been significantly reduced, and its drying behavior has changed from "rapid removal of a large amount of solvent" to "slow migration of residual solvent," which is kinetically more compatible with the first drying behavior of the composite adhesive. When the composite adhesive is applied to the lower surface of the aluminum foil, it is in a fully wet state with the highest solvent content. In the low-temperature evaporation zone of the first drying, it undergoes a solvent removal process similar to that after the flash drying of the high-temperature coating. Since most of the solvent has been removed from the high-temperature coating, the difference in solvent evaporation rate between the two coatings in each temperature zone of the first drying is reduced, and the unified temperature curve can take into account both sides at the same time.

[0041] Secondly, the semi-dry film provides a thermal buffer for the high-temperature resistant coating, avoiding the imbalance of thermal response on both sides during the initial drying stage. After flash drying, the surface resin of the high-temperature resistant coating has undergone preliminary cross-linking, forming a low-cross-linking density network structure. This film will not immediately soften or melt in the low-temperature volatile zone of the initial drying stage, but will maintain a stable solid skeleton. When heat is conducted from the upper surface of the aluminum foil to the high-temperature resistant coating, the thermal resistance of the film slows down the heating rate inside the coating, making it more synchronized with the heating rate of the composite adhesive side as heat is conducted from the lower surface of the aluminum foil to the composite adhesive. If the high-temperature resistant coating enters the initial drying stage directly without flash drying, the thermal conductivity of the wet coating is higher than that of the dry coating. The rapid heat transfer causes the surface solvent to boil violently, creating a significant temperature difference with the gradual heating of the composite adhesive side, resulting in uneven thermal expansion on both sides of the aluminum foil. The semi-dry film after flash drying makes the heating curves on both sides more consistent, and the thermal stress symmetrical.

[0042] Third, both resin systems use acrylic resins of the same chemical group but different molecular weights, resulting in overlapping curing temperature windows. Both the high-temperature coating and the composite adhesive use acrylic resin as the matrix. The high-temperature coating uses low molecular weight acrylic resin (5000-15000) with a lower glass transition temperature and a crosslinking reaction initiation temperature of approximately 100-120℃; the composite adhesive uses high molecular weight acrylic resin (20000-50000) with a higher glass transition temperature and a crosslinking reaction initiation temperature of approximately 110-130℃. Since their crosslinking temperature windows overlap in the 100-130℃ range, during the initial drying and medium-temperature curing zone (100-130℃), both resins simultaneously enter the crosslinking reaction stage. The low molecular weight resin crosslinks faster, forming a dense network first, while the high molecular weight resin gradually entangles and crosslinks subsequently. Both coatings transition from a liquid to a solid state synchronously, eliminating the time difference between one side being fully cured and the other still in a swollen state. If different chemical groups of resin are used on both sides (such as acrylic on one side and polyurethane on the other), the curing temperature windows may not overlap at all, making it impossible to find a uniform primary drying temperature profile.

[0043] Fourth, the PET / PP pre-composite film is introduced as an integral substrate, and its thermal stability supports the high-temperature zone of the primary drying process. In existing technologies, if a PP film is directly laminated to the lower surface of an aluminum foil, the heat distortion temperature of the PP film is approximately 120-150℃, and it may soften and deform in the high-temperature setting zone (150-180℃) during primary drying. However, in this application, the PP film is pre-laminated with the PET film to form an integral whole. The heat resistance of the PET film is superior to that of the PP film (PET melting point is approximately 250℃), and the PET film is located between the composite adhesive layer and the PP film. During primary drying, the PET film acts as a heat buffer layer, preventing the heat from the aluminum foil from being directly conducted to the PP film. The actual temperature that the PP film withstands is lower than its heat distortion temperature, and it will not soften due to the high-temperature zone of primary drying. This allows the high-temperature setting zone of primary drying to be set at 150-180℃, meeting the requirements for complete curing of the high-temperature resistant coating without damaging the heat-sealing performance of the PP film.

[0044] Fifth, the aluminum foil itself acts as a heat conductor, playing a role in achieving thermal equilibrium on both sides during the primary drying process. With a thickness of 0.04-0.08 mm and a thermal conductivity of approximately 200 W / (m·K), the aluminum foil's upper and lower surfaces are heated simultaneously in the primary drying oven. Heat is rapidly conducted laterally through the foil, resulting in a more uniform overall temperature. The temperature difference between the two coatings is smoothed out by the aluminum foil's thermal conductivity, preventing extreme situations of one side being overheated and the other underheated. The high-temperature resistant coating film after flash drying has moderate thermal resistance and does not hinder the thermal equilibrium effect of the aluminum foil. If the high-temperature resistant coating is completely wet, although its thermal conductivity is high, the heat consumption from solvent evaporation is significant, and localized areas may experience a sudden temperature drop due to solvent boiling, disrupting the thermal equilibrium.

[0045] In summary, the flash-dried semi-dry film state pre-reduces the solvent load of the high-temperature resistant coating and provides a thermal buffer. The overlapping temperature windows of the resin systems on both sides ensure synchronous cross-linking. The overall heat resistance of the PET / PP pre-composite film supports high-temperature setting. The thermal conductivity effect of the aluminum foil balances the temperature difference on both sides. The synergistic effect of these four mechanisms enables the coatings on both sides to be successfully cured simultaneously in a single heating and drying process. Furthermore, the thermal stress on both sides of the aluminum foil is symmetrical, warpage is suppressed, the cumulative heating time of the aluminum foil is shortened, grain growth is inhibited, and tensile strength and elongation remain excellent.

[0046] A second aspect of the present invention provides an aluminum-plastic composite sealing film, which is prepared by the above-described method for preparing aluminum-plastic composite sealing film.

[0047] The following are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention.

[0048] Example 1

[0049] A method for preparing an aluminum-plastic composite sealing film includes the following steps: (1) Preparation of PET / PP pre-composite film: A food-grade PET film with a thickness of 0.015 mm is subjected to double-sided corona treatment with a corona value of 40 dynes; a first composite adhesive is coated on one side of the PET film using a gravure roller coating method. The first composite adhesive is a polyurethane dry composite adhesive with a coating amount of 3 g / m², forming a first composite adhesive layer; a food-grade PP film with a thickness of 0.035 mm is laminated onto the first composite adhesive layer, so that the PP film is in contact with the first composite adhesive layer; the PET film and PP film are heated and dried at a temperature of 100℃ for 8 seconds to cure the first composite adhesive layer and form a PET / PP pre-composite film.

[0050] (2) Unwinding aluminum foil: Unwind aluminum foil with a thickness of 0.06mm onto the machine at a speed of 55m / min and a tension of 9kg.

[0051] (3) High temperature resistant coating: A two-component varnish is applied to the upper surface of the aluminum foil using a gravure roller coating method. The two-component varnish includes acrylic resin and curing agent. The acrylic resin has a molecular weight of 10,000 and contains hydroxyl and carboxyl functional groups. The coating amount is 1.5 g / m², forming a high temperature resistant coating.

[0052] (4) Flash baking: The high-temperature resistant coating is flash baked using far-infrared radiation heating with a wavelength of 3.5 μm and a radiation intensity of 65 kW / m². The flash baking time is 2 seconds. After flash baking, the surface temperature of the high-temperature resistant coating is 90°C and the surface is in a semi-dry film state. The semi-dry film is judged by the criterion that it is not sticky to the touch and can be scratched with a fingernail. There is no cooling step between flash baking and subsequent composite adhesive coating.

[0053] (5) Composite adhesive coating and PET / PP pre-composite film lamination: The composite adhesive is coated on the lower surface of the aluminum foil using a direct coating method. The composite adhesive includes acrylic resin and ethyl acetate solvent, wherein the molecular weight of the acrylic resin is 35,000, and it has epoxy and amino functional groups. The coating amount is 5 g / m². The PET / PP pre-composite film is laminated onto the composite adhesive, so that the PET surface is in contact with the composite adhesive. The lamination pressure is 5.5 kg. The solvent in the composite adhesive is miscible with the residual solvent on the surface of the high-temperature resistant coating. The high molecular weight acrylic resin in the composite adhesive penetrates into the surface of the high-temperature resistant coating, and the low molecular weight acrylic resin in the high-temperature resistant coating diffuses into the bottom layer of the composite adhesive, forming an interpenetrating transition layer with a thickness of about 1.0 μm.

[0054] (6) Primary Heating and Drying: The aluminum foil undergoes primary heating and drying using a gradient heating method, consisting of a low-temperature evaporation zone, a medium-temperature curing zone, and a high-temperature setting zone. The low-temperature evaporation zone has a temperature of 70℃, a duration of 45% of the total primary heating and drying time, and a dwell time of 6 seconds; the medium-temperature curing zone has a temperature of 115℃, a duration of 35% of the total primary heating and drying time, and a dwell time of 5 seconds; the high-temperature setting zone has a temperature of 165℃, a duration of 20% of the total primary heating and drying time, and a dwell time of 3 seconds. During the primary heating and drying process, a blowing device is installed on one side of the upper surface of the aluminum foil, blowing an airflow at a temperature of 50℃ at a speed of 6.5 m / s; a suction device is installed on one side of the lower surface of the aluminum foil, with a speed of 4 m / s. There is no pre-drying step before the primary heating and drying.

[0055] In the high-temperature setting zone, the hydroxyl and carboxyl groups in the high-temperature resistant coating undergo a condensation reaction with the epoxy and amino groups in the composite adhesive to form chemical bonds, and the interpenetrating transition layer is transformed into a covalent bonded interface.

[0056] (7) Cooling: The dried aluminum foil is cooled by cold air and cooling roller. The temperature of the aluminum foil after cooling is 40℃, the pressure of the cooling roller is 5.5kg, and the temperature of the cooling roller is 22℃.

[0057] (8) Aluminum foil winding: The winding tension is 11 kg.

[0058] The prepared aluminum-plastic composite sealing film was examined by scanning electron microscopy. The thickness of the interpenetrating transition layer between the high-temperature resistant coating and the aluminum foil layer was 1.0 μm. In a 180° peel strength test, the peel strength between the high-temperature resistant coating and the aluminum foil layer was 26 N / 15 mm, and the peel strength between the aluminum foil layer and the PET / PP pre-composite film was 24 N / 15 mm. The aluminum foil underwent a tensile test, showing a tensile strength of 185 MPa and an elongation at break of 3.2%. The aluminum-plastic composite sealing film was stamped with tinplate to form an easy-tear cap. After steaming at 119°C for 75 minutes, the easy-tear cap had an opening force of 4.5 N, and its sealing performance showed no degradation.

[0059] Example 2

[0060] A method for preparing an aluminum-plastic composite sealing film includes the following steps: (1) Preparation of PET / PP pre-composite film: A food-grade PET film with a thickness of 0.015 mm is subjected to double-sided corona treatment with a corona value of 42 dynes; a first composite adhesive is coated on one side of the PET film by direct coating method. The first composite adhesive is a polyurethane dry composite adhesive with a coating amount of 2.5 g / m², forming a first composite adhesive layer; a food-grade PP film with a thickness of 0.035 mm is laminated on the first composite adhesive layer, so that the PP film is in contact with the first composite adhesive layer; the PET film and PP film are heated and dried at a temperature of 90°C for 10 seconds to cure the first composite adhesive layer and form a PET / PP pre-composite film.

[0061] (2) Unwinding aluminum foil: Unwind aluminum foil with a thickness of 0.05mm onto the machine at a speed of 50m / min and a tension of 8kg.

[0062] (3) High temperature resistant coating: A two-component varnish is applied to the upper surface of the aluminum foil by a direct scraping method. The two-component varnish includes acrylic resin and curing agent. The acrylic resin has a molecular weight of 5000 and contains hydroxyl and carboxyl functional groups. The coating amount is 1.2g / m², forming a high temperature resistant coating.

[0063] (4) Flash baking: The high-temperature resistant coating is flash baked using far-infrared radiation heating with a wavelength of 3μm and a radiation intensity of 50kW / m². The flash baking time is 3 seconds. After flash baking, the surface temperature of the high-temperature resistant coating is 80℃ and the surface is in a semi-dry film state. There is no cooling step between flash baking and subsequent composite adhesive coating.

[0064] (5) Composite adhesive coating and PET / PP pre-composite film lamination: Composite adhesive is coated on the lower surface of aluminum foil using a gravure roller coating method. The composite adhesive includes acrylic resin and ethyl acetate solvent, wherein the molecular weight of acrylic resin is 20,000, and it contains epoxy and amino functional groups. The coating amount is 4 g / m². The PET / PP pre-composite film is laminated onto the composite adhesive, so that the PET side is in contact with the composite adhesive. The lamination pressure is 5 kg. Heat-sealing adhesive is coated on the lower surface of the aluminum foil corresponding to the high-temperature resistant coating in the semi-dry film state to form an interpenetrating transition layer with a thickness of about 0.8 μm.

[0065] (6) Primary Heating and Drying: The aluminum foil is subjected to primary heating and drying using a gradient heating method. The low-temperature volatile zone has a temperature of 60℃, a duration of 50% of the total primary heating and drying time, and a dwell time of 8 seconds; the medium-temperature curing zone has a temperature of 100℃, a duration of 30% of the total primary heating and drying time, and a dwell time of 5 seconds; the high-temperature setting zone has a temperature of 150℃, a duration of 20% of the total primary heating and drying time, and a dwell time of 3 seconds. During the primary heating and drying process, a blowing device is installed on one side of the upper surface of the aluminum foil, blowing an airflow at a temperature of 40℃ with a wind speed of 5m / s; a suction device is installed on one side of the lower surface of the aluminum foil with a wind speed of 3m / s. There is no pre-drying step before the primary heating and drying.

[0066] In the high-temperature setting zone, the hydroxyl and carboxyl groups in the high-temperature resistant coating undergo a condensation reaction with the epoxy and amino groups in the composite adhesive to form chemical bonds.

[0067] (7) Cooling: The dried aluminum foil is cooled by cold air and cooling roller. The temperature of the aluminum foil after cooling is 35℃, the pressure of the cooling roller is 5kg, and the temperature of the cooling roller is 20℃.

[0068] (8) Aluminum foil winding: The winding tension is 10kg.

[0069] The prepared aluminum-plastic composite sealing film was examined by scanning electron microscopy. The thickness of the interpenetrating transition layer between the high-temperature resistant coating and the aluminum foil layer was 0.8 μm. In a 180° peel strength test, the peel strength between the high-temperature resistant coating and the aluminum foil layer was 24 N / 15 mm, and the peel strength between the aluminum foil layer and the PET / PP pre-composite film was 22 N / 15 mm. The aluminum foil underwent a tensile test, showing a tensile strength of 190 MPa and an elongation at break of 3.5%. The aluminum-plastic composite sealing film was stamped with tinplate to form an easy-tear cap. After steaming at 119°C for 75 minutes, the easy-tear cap had an opening force of 4.2 N, and its sealing performance showed no degradation.

[0070] Example 3

[0071] A method for preparing an aluminum-plastic composite sealing film includes the following steps: (1) Preparation of PET / PP pre-composite film: A food-grade PET film with a thickness of 0.015 mm is subjected to double-sided corona treatment with a corona value of 45 dynes; a first composite adhesive is coated on one side of the PET film using an anilox roller coating method. The first composite adhesive is a polyurethane dry composite adhesive with a coating amount of 4 g / m², forming a first composite adhesive layer; a food-grade PP film with a thickness of 0.035 mm is laminated onto the first composite adhesive layer, so that the PP film is in contact with the first composite adhesive layer; the PET film and PP film are heated and dried at a temperature of 110℃ for 6 seconds to cure the first composite adhesive layer and form a PET / PP pre-composite film.

[0072] (2) Unwinding aluminum foil: Unwind aluminum foil with a thickness of 0.07mm onto the machine at a speed of 60m / min and a tension of 10kg.

[0073] (3) High temperature resistant coating: A two-component varnish is applied to the upper surface of the aluminum foil using a gravure roller coating method. The two-component varnish includes acrylic resin and curing agent. The acrylic resin has a molecular weight of 15,000 and contains hydroxyl and carboxyl functional groups. The coating amount is 1.8 g / m², forming a high temperature resistant coating.

[0074] (4) Flash baking: The high-temperature resistant coating is flash baked using far-infrared radiation heating with a wavelength of 4μm and a radiation intensity of 80kW / m². The flash baking time is 1 second. After flash baking, the surface temperature of the high-temperature resistant coating is 100℃ and the surface is in a semi-dry film state. There is no cooling step between flash baking and subsequent composite adhesive coating.

[0075] (5) Composite adhesive coating and PET / PP pre-composite film lamination: The composite adhesive is coated on the lower surface of the aluminum foil using a direct coating method. The composite adhesive includes acrylic resin and ethyl acetate solvent, wherein the acrylic resin has a molecular weight of 50,000 and contains epoxy and amino functional groups, and the coating amount is 6 g / m². The PET / PP pre-composite film is laminated onto the composite adhesive, so that the PET side is in contact with the composite adhesive, and the lamination pressure is 6 kg. The composite adhesive is coated on the lower surface of the aluminum foil corresponding to the high-temperature resistant coating in the semi-dry film state, forming an interpenetrating transition layer with a thickness of about 1.5 μm.

[0076] (6) Primary Heating and Drying: The aluminum foil is subjected to primary heating and drying using a gradient heating method. The temperature of the low-temperature volatile zone is 80℃, the duration is 40% of the total primary heating and drying time, and the dwell time is 5 seconds; the temperature of the medium-temperature curing zone is 130℃, the duration is 40% of the total primary heating and drying time, and the dwell time is 5 seconds; the temperature of the high-temperature setting zone is 180℃, the duration is 20% of the total primary heating and drying time, and the dwell time is 3 seconds. During the primary heating and drying process, a blowing device is installed on one side of the upper surface of the aluminum foil, blowing an airflow at a temperature of 60℃ with a wind speed of 8m / s; a suction device is installed on one side of the lower surface of the aluminum foil with a wind speed of 5m / s. There is no pre-drying step before the primary heating and drying.

[0077] In the high-temperature setting zone, the hydroxyl and carboxyl groups in the high-temperature resistant coating undergo a condensation reaction with the epoxy and amino groups in the composite adhesive to form chemical bonds.

[0078] (7) Cooling: The dried aluminum foil is cooled by cold air and cooling roller. The temperature of the aluminum foil after cooling is 45℃, the pressure of the cooling roller is 6kg, and the temperature of the cooling roller is 25℃.

[0079] (8) Aluminum foil winding: The winding tension is 12kg.

[0080] The prepared aluminum-plastic composite sealing film was examined by scanning electron microscopy. The thickness of the interpenetrating transition layer between the high-temperature resistant coating and the aluminum foil layer was 1.5 μm. In a 180° peel strength test, the peel strength between the high-temperature resistant coating and the aluminum foil layer was 25 N / 15 mm, and the peel strength between the aluminum foil layer and the PET / PP pre-composite film was 23 N / 15 mm. The aluminum foil underwent a tensile test, showing a tensile strength of 182 MPa and an elongation at break of 3.0%. The aluminum-plastic composite sealing film was stamped with tinplate to form an easy-tear cap. After being steamed at 119°C for 75 minutes, the easy-tear cap had an opening force of 4.8 N, and its sealing performance showed no degradation.

[0081] It should be noted that the test samples for the peel strength were all 15 mm wide as the test reference.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an aluminum-plastic composite sealing film, wherein the aluminum-plastic composite sealing film comprises, from top to bottom, a high-temperature resistant coating, an aluminum foil, a composite adhesive layer, a PET film, another composite adhesive layer, and a PP film; characterized in that, The preparation method includes the following steps: The PET film and PP film are pre-composite to form a PET / PP pre-composite film; Aluminum foil unwinding; A high-temperature resistant coating is applied to the upper surface of the aluminum foil to form a high-temperature resistant coating. The high-temperature resistant coating is flash-baked using infrared radiation heating with a radiation wavelength of 2-4μm, a radiation intensity of 50-80kW / m², and a flash-baking time of 1-3 seconds. After flash-baking, the surface temperature of the high-temperature resistant coating is 80-100℃ and the surface is in a semi-dry film state. A composite adhesive is applied to the lower surface of the aluminum foil, and the PET / PP pre-composite film is laminated onto the composite adhesive, so that the PET side is in contact with the composite adhesive; The aluminum foil is subjected to a single heating and drying process to simultaneously cure the high-temperature resistant coating and the composite adhesive. The temperature of the single heating and drying process does not exceed 180°C. The dried aluminum foil is cooled and then wound up.

2. The method for preparing the aluminum-plastic composite sealing film according to claim 1, characterized in that, The specific steps for pre-compositing the PET film and the PP film to form a PET / PP pre-composite film are as follows: coating a composite adhesive on one side of the PET film to form a first composite adhesive layer; laminating the PP film onto the first composite adhesive layer so that the PP film is in contact with the first composite adhesive layer; heating and drying the PET film and the PP film to cure the first composite adhesive layer and form the PET / PP pre-composite film.

3. The method for preparing the aluminum-plastic composite sealing film according to claim 2, characterized in that, The PET film has a thickness of 0.015 mm, and the PP film has a thickness of 0.035 mm. The PET film is subjected to double-sided corona treatment before pre-lamination, and the corona value is not less than 38 dynes. The coating amount of the first composite adhesive is 2-4 g / m². The heating and drying temperature is 80-120℃, and the drying time is 5-10 seconds.

4. The method for preparing the aluminum-plastic composite sealing film according to claim 1, characterized in that, The primary heating and drying process employs a gradient temperature increase method, which sequentially includes a low-temperature volatilization zone, a medium-temperature curing zone, and a high-temperature setting zone. The temperature of the low-temperature volatilization zone is 60-80℃, the temperature of the medium-temperature curing zone is 100-130℃, and the temperature of the high-temperature setting zone is 150-180℃.

5. The method for preparing the aluminum-plastic composite sealing film according to claim 4, characterized in that, The duration of the low-temperature volatilization zone is 40%-50% of the total duration of the single heating and drying, the duration of the medium-temperature curing zone is 30%-40% of the total duration of the single heating and drying, and the duration of the high-temperature setting zone is 10%-20% of the total duration of the single heating and drying.

6. The method for preparing the aluminum-plastic composite sealing film according to claim 1, characterized in that, During the first heating and drying process, a blowing device is provided on one side of the upper surface of the aluminum foil, which blows an airflow at a temperature of 40-60℃ and a wind speed of 5-8m / s; a suction device is provided on one side of the lower surface of the aluminum foil, which has a wind speed of 3-5m / s.

7. The method for preparing the aluminum-plastic composite sealing film according to claim 1, characterized in that, The high-temperature resistant coating comprises a two-component varnish, which includes an acrylic resin and a curing agent. The composite adhesive comprises an acrylic resin and a solvent. The acrylic resin in the high-temperature resistant coating has a molecular weight of 5,000-15,000, and the acrylic resin in the composite adhesive has a molecular weight of 20,000-50,000.

8. The method for preparing the aluminum-plastic composite sealing film according to claim 7, characterized in that, The acrylic resin in the high-temperature resistant coating has hydroxyl and carboxyl functional groups, and the acrylic resin in the composite adhesive has epoxy and amino functional groups. The high-temperature resistant coating in the semi-dry film state and the composite adhesive undergo a condensation reaction in the high-temperature setting zone to form a chemical bond.

9. The method for preparing the aluminum-plastic composite sealing film according to claim 1, characterized in that, The flash drying process uses far-infrared radiation heating, with a wavelength of 3-4 μm, a radiation intensity of 60-70 kW / m², a flash drying time of 1.5-2.5 seconds, and a surface temperature of 85-95℃ after flash drying of the high-temperature resistant coating.

10. An aluminum-plastic composite sealing film, characterized in that, The aluminum-plastic composite sealing film is prepared by the method for preparing aluminum-plastic composite sealing film according to any one of claims 1-9.

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