Aluminum foil packaged meal box and manufacturing method thereof

Abstract

The invention belongs to the technical field of aluminum foil lunch boxes, and discloses an aluminum foil packaged lunch box and a manufacturing method thereof.The aluminum foil packaged lunch box is obtained by conducting punch forming on a composite base material in a mold, and the composite base material sequentially comprises an inner contact layer, an aluminum foil core layer and a reinforcing layer from inside to outside; first adhesion layers are arranged between the inner contact layer and the aluminum foil core layer and between the aluminum foil core layer and the enhancement layer; wherein the aluminum foil core layer is formed by calendering and compounding at least three aluminum foil layers, a second adhesion layer is arranged between every two adjacent aluminum foil layers, and the aluminum foil layers comprise, by mass, 0.05%-0.15% of Si, 0.40%-0.50% of Fe, 0.12%-0.20% of Cu, 0.08%-0.10% of Mg, smaller than or equal to 0.05% of Mn, smaller than or equal to 0.05% of Zn, smaller than or equal to 0.03% of a single impurity element and the balance Al. Through innovative design of a composite base material structure and precise regulation and control of a forming process, comprehensive improvement of the comprehensive performance of the aluminum foil packaging meal box is achieved, and the industrial defects that a traditional aluminum foil meal box is poor in deformation resistance, interlayer stripping is prone to occurring, and the sealing performance is poor are effectively overcome.

Description

Technical Field

[0001] This invention belongs to the field of aluminum foil lunch box technology, and specifically relates to an aluminum foil packaging lunch box and its manufacturing method. Background Technology

[0002] Aluminum foil packaging containers have become indispensable in daily dining due to their lightweight, excellent thermal conductivity, recyclability, and ability to preserve food flavor. They are widely used in various fields such as food delivery, food preservation, and convenient catering. However, existing aluminum foil packaging containers still have significant performance shortcomings in actual use, especially in complex transportation scenarios such as food delivery.

[0003] Traditional aluminum foil lunch boxes mostly use a single layer of aluminum foil or a few simple two-layer composite structures. The mechanical strength of aluminum foil itself is limited, and there is a lack of effective coordinating force-bearing design between the layers. Relying solely on the rigidity of the aluminum foil itself is insufficient to withstand external forces such as compression and collisions during transportation. At the same time, the material combination of existing lunch boxes lacks systematic consideration. Either the flexibility and rigidity of the materials are mismatched, making the structure prone to loosening due to differences in deformation under stress, or the external protection performance is insufficient, failing to effectively protect the core supporting structure, further weakening the overall deformation resistance of the lunch box. In addition, the connection methods of the various structural parts of existing lunch boxes have defects, making it difficult to achieve a stable connection. Loosening or even separation can easily occur, causing the lunch box to fail to form a coordinating whole under stress. Local stress concentration can easily lead to wrinkling of the side walls, denting of the bottom, or even cracking, ultimately causing the soup inside the lunch box to leak. This not only affects food hygiene and eating experience but may also cause contamination problems during transportation. Summary of the Invention

[0004] The present invention aims to improve at least one technical problem in the prior art.

[0005] This invention provides an aluminum foil packaged lunch box, which is formed by stamping a composite substrate in a mold. The composite substrate includes an inner contact layer, an aluminum foil core layer and a reinforcing layer from the inside to the outside. A first adhesive layer is provided between the inner contact layer and the aluminum foil core layer and between the aluminum foil core layer and the reinforcing layer. The inner contact layer is formed of polyethylene; The reinforcing layer is formed of a hydrogenated styrene-butadiene block copolymer; The aluminum foil core layer is formed by rolling and laminating at least three layers of aluminum foil, with a second adhesive layer between adjacent aluminum foil layers. The composition of the aluminum foil layers, by mass percentage, is: Si 0.05%-0.15%, Fe 0.40%-0.50%, Cu 0.12%-0.20%, Mg 0.08%-0.10%, Mn ≤0.05%, Zn ≤0.05%, single impurity element ≤0.03%, and the balance being Al. Both the first adhesive layer and the second adhesive layer are polyurethane resins.

[0006] The aluminum foil packaging lunch box of this application constructs a synergistic overall structure through precise matching of the structural layers and adhesive layers of the composite substrate. This solves the problems of weak resistance to extrusion deformation and easy leakage of traditional aluminum foil lunch boxes, while ensuring food contact safety and molding stability. The inner contact layer is made of polyethylene material, which has both excellent food compatibility and moderate flexibility. It can not only avoid harmful migration when in contact with food, ensuring food safety, but also adapt to the rigidity of the aluminum foil core layer during the stamping process, reducing the risk of interlayer peeling due to differences in material hardness. At the same time, it provides a smooth surface for the inner wall of the aluminum foil packaging lunch box, avoiding scratches on the food packaging. In this application, the aluminum foil core layer, as the core load-bearing structure of the aluminum foil packaged lunch box, is composed of at least three layers of aluminum foil. This multi-layered design significantly improves the structural rigidity and compressive strength. The second adhesive layer between adjacent aluminum foil layers utilizes the excellent bonding properties of polyurethane resin to ensure that each aluminum foil layer is tightly bonded into a unified load-bearing body, effectively dispersing local compressive stress during transportation and avoiding the defects of single-layer aluminum foil being easily deformed and broken. Combined with the high strength inherent in the specific composition ratio of the aluminum foil layers, the aluminum foil core layer achieves a balance between rigidity and toughness, stably supporting the shape of the aluminum foil packaged lunch box while resisting minor impacts without easily breaking. The reinforcing layer uses hydrogenated styrene-butadiene block copolymer, whose excellent elasticity and impact resistance complement the rigidity of the aluminum foil core layer. When the aluminum foil packaged lunch box is subjected to external impact or compression, the reinforcing layer can quickly absorb the impact energy, inhibiting the transmission of stress to the aluminum foil core layer, thereby reducing wrinkling of the side walls and deformation of the bottom of the aluminum foil packaged lunch box, and significantly improving the overall deformation resistance. The first adhesive layer, serving as a crucial connecting carrier, is also made of polyurethane resin. It not only forms a stable bond with the polyethylene of the inner contact layer and the aluminum foil material of the aluminum foil core layer, but also achieves a strong bond with the hydrogenated styrene-butadiene block copolymer of the reinforcing layer. This allows the composite substrate to form a complete, layer-free structure from the inside out, ensuring that each layer works in synergy under stress. The flexibility of the inner contact layer buffers the rigid impact of the aluminum foil core layer through the corresponding first adhesive layer, while the elasticity of the reinforcing layer assists the aluminum foil core layer in dispersing stress through the corresponding first adhesive layer. The rigidity of the aluminum foil core layer provides stable support for the inner contact layer and the reinforcing layer. The three layers complement each other through the connecting effect of the first adhesive layer, ultimately giving the aluminum foil packaging lunch box the core characteristics of high strength, compression resistance, and leak prevention, making it fully suitable for the use needs of complex transportation scenarios such as food delivery.

[0007] In some preferred embodiments, the composition of the aluminum foil layer, by mass percentage, is: Si 0.08%-0.12%, Fe 0.43%-0.47%, Cu 0.15%-0.18%, Mg 0.09%-0.10%, Mn ≤0.03%, Zn ≤0.03%, individual impurity elements ≤0.02%, and the balance is Al with a mass percentage ≥99.2%.

[0008] In some preferred embodiments, the thickness of the aluminum foil layer is 0.03mm-0.05mm, the thickness of the second adhesive layer is 2μm-4μm, and the thickness of the aluminum foil core layer is 0.09mm-0.15mm.

[0009] The above-mentioned method for preparing the aluminum foil core layer includes the following steps: According to the aluminum foil layer composition design, weigh the corresponding raw materials, mix, melt, refine, cast, and cold roll to obtain the aluminum foil layer; Take at least 3 layers of the aluminum foil, coat the polyurethane resin between adjacent aluminum foil layers, and then perform the calendering and lamination to obtain the aluminum foil core layer; The rolling temperature of the calendered composite is 80℃-100℃, and the rolling pressure is 3MPa-5MPa.

[0010] The method for preparing the aluminum foil core layer in this application provides a high-strength, highly uniform core support structure for aluminum foil packaging lunch boxes through precise control and coordinated operation of each process step, ensuring the overall performance of the composite substrate from a process perspective. First, the raw materials are precisely weighed and mixed according to the composition design of the aluminum foil layer, ensuring that the proportions of each alloying element meet the strength requirements, laying the foundation for the mechanical properties of the aluminum foil layer itself. Subsequent melting and refining processes effectively remove impurities and gases from the raw materials, improving the purity of the aluminum alloy liquid and preventing impurities or bubbles from affecting the structural integrity of the aluminum foil layer. The casting and cold rolling processes, by gradually controlling the thickness, obtain a uniform thickness and dense texture of the aluminum foil layer, ensuring that each layer of aluminum foil possesses consistent strength and toughness, thus guaranteeing the structural stability of the multi-layer composite. In the multi-layer aluminum foil lamination stage, polyurethane resin is coated between adjacent aluminum foil layers. Then, synchronous calendering lamination is performed using a rolling temperature of 80℃-100℃ and a rolling pressure of 3MPa-5MPa. This temperature range allows the polyurethane resin to maintain suitable fluidity and viscosity, ensuring uniform coverage of the aluminum foil surface while preventing resin performance degradation due to excessive temperature. The specific rolling pressure promotes the full utilization of intermolecular forces between the aluminum foil layers and the resin, as well as between the aluminum foil layers themselves, achieving a bubble-free, tight bond and effectively avoiding uneven thickness caused by localized overlap. This multi-layer co-calendering process allows at least three aluminum foil layers to form a unified stress-bearing whole under the action of the adhesive layer. Compared to single-layer aluminum foil, this not only results in a more uniform thickness but also significantly improves the overall strength, toughness, and puncture resistance of the aluminum foil core layer through interlayer stress synergy. This provides a stable and reliable material foundation for the subsequent deep-drawing molding of aluminum foil packaging food boxes, ensuring that the molded aluminum foil packaging food boxes can withstand the squeezing and impact in scenarios such as food delivery, reducing the risk of deformation and leakage.

[0011] In some preferred embodiments, the hydrogenated styrene-butadiene block copolymer is obtained by block polymerization of styrene monomer and butadiene monomer in a mass ratio of (25-35):(65-75).

[0012] In some preferred embodiments, the thickness of the inner contact layer is 6μm-8μm, the thickness of the reinforcing layer is 5μm-6μm, and the thickness of the first adhesive layer is 2μm-4μm.

[0013] The present invention also provides a method for manufacturing the above-mentioned aluminum foil packaged lunch box, comprising the following steps: The polyurethane resin is coated between the inner contact layer and the aluminum foil core layer, and between the aluminum foil core layer and the reinforcing layer. Then, the substrate is placed in the mold, the bottom temperature of which is controlled at 30℃-40℃ and the side wall temperature of which is controlled at 60℃-80℃. The composite substrate is then stamped, trimmed, and cleaned to obtain the aluminum foil packaging lunch box.

[0014] This application employs gradient temperature-controlled stamping. The bottom of the mold is set at a relatively low temperature of 30℃-40℃, which effectively suppresses excessive stretching of the inner contact layer (polyethylene) and aluminum foil core layer during stamping, preventing the bottom of the aluminum foil packaging box from losing strength due to material thinning and eliminating the risk of breakage. Meanwhile, the mold sidewalls are moderately heated at 60℃-80℃, which reduces the yield strength of the aluminum foil core layer while improving the flexibility of the inner contact layer and the elastic flow of the reinforcing layer (hydrogenated styrene-butadiene block copolymer). This allows the composite substrate to extend evenly along the mold sidewalls during stretching, effectively preventing wrinkling or excessive local thickness deviations in the aluminum foil packaging box sidewalls. This zoned temperature control design precisely adapts to the material characteristics of each layer of the composite substrate, enabling the rigid aluminum foil core layer, flexible inner contact layer, and elastic reinforcing layer to work together during molding. This allows for one-time molding of aluminum foil packaging boxes with greater depth and strict control over wall thickness uniformity.

[0015] The stamping pressure is 6MPa-10MPa, and the holding time is 10s-18s.

[0016] The beneficial effects of this invention are as follows: Through innovative design of the composite substrate structure and precise control of the molding process, this invention achieves a comprehensive improvement in the overall performance of aluminum foil packaging lunch boxes, effectively solving industry pain points such as weak deformation resistance, easy peeling between layers, and poor sealing performance of traditional aluminum foil lunch boxes. The composite structure of multiple aluminum foil core layers, combined with a special adhesive layer, makes each aluminum foil layer form a unified whole that works synergistically, significantly enhancing the rigidity and toughness of the lunch box. Simultaneously, the design of aluminum foil layers with specific compositions further solidifies the core mechanical performance foundation of the lunch box. The material selection and structural adaptation of the inner contact layer and the reinforcing layer ensure both food contact safety and user comfort, while the elastic properties of the reinforcing layer complement the performance of the aluminum foil core layer, improving the impact resistance of the lunch box. The application of gradient temperature-controlled stamping molding process optimizes the material flow state of the composite substrate during molding, ensuring uniform wall thickness and structural stability of the lunch box. This avoids defects such as localized thinning and wrinkling from a process perspective, improving the sealing integrity of the lunch box. Overall, the aluminum foil packaging lunch box of the present invention has the core advantages of high strength, compression resistance and leakage prevention, while meeting food contact safety standards. It can fully adapt to the needs of complex usage scenarios such as food delivery, and has significant practical value and promotion prospects. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0018] The raw materials used in the following examples and comparative examples are all food grade.

[0019] Example 1 An aluminum foil packaged lunch box is formed by stamping a composite substrate in a mold. The composite substrate includes an inner contact layer, an aluminum foil core layer and a reinforcing layer from the inside to the outside. A first adhesive layer is provided between the inner contact layer and the aluminum foil core layer and between the aluminum foil core layer and the reinforcing layer.

[0020] The first adhesive layer is made of polyurethane resin and has a thickness of 3 μm.

[0021] The inner contact layer is made of polyethylene and has a thickness of 7 μm.

[0022] The reinforcing layer is formed by hydrogenated styrene-butadiene block copolymer, which is obtained by block polymerization of styrene monomer and butadiene monomer in a mass ratio of 30:70; the thickness of the reinforcing layer is 6 μm.

[0023] The aluminum foil core layer is formed by rolling and laminating three layers of aluminum foil. A second adhesive layer is provided between adjacent aluminum foil layers. The composition of the aluminum foil layers, by mass percentage, is: Si 0.10%, Fe 0.45%, Cu 0.16%, Mg 0.09%, Mn The aluminum foil core layer consists of 0.02% Zn, 0.03% Zn, and ≤0.02% Zn for each individual impurity element, with the balance being Al. The second adhesive layer is polyurethane resin. The aluminum foil layer has a thickness of 0.04 mm, the second adhesive layer has a thickness of 3 μm, and the aluminum foil core layer has a thickness of 0.10 mm. The preparation method of the aluminum foil core layer includes the following steps: weigh the corresponding raw materials according to the aluminum foil layer composition design, mix them, melt them at 750℃ for 40 min, add a refining agent at 750℃ and refine them for 20 min, cast and roll them at a speed of 900 mm / min (roller surface temperature is 90℃), and cold roll them at a speed of 6 m / min (roller surface temperature is 25℃) to obtain the aluminum foil layer. Take 3 aluminum foil layers, coat polyurethane resin between adjacent aluminum foil layers, and then perform calendering and compounding (roller pressing temperature is 90℃, roller pressing pressure is 5 MPa, and roller pressing speed is 5 m / min) to obtain the aluminum foil core layer.

[0024] The method for manufacturing this aluminum foil-wrapped lunch box includes the following steps: Polyurethane resin is coated between the inner contact layer and the aluminum foil core layer, and between the aluminum foil core layer and the reinforcing layer. Then, it is placed in a mold with the bottom temperature of the mold controlled at 35°C and the side wall temperature of the mold controlled at 80°C. The composite substrate is stamped (the stamping pressure is 8MPa and the holding time is 10s), trimmed, and cleaned to obtain an aluminum foil packaged lunch box.

[0025] Example 2 An aluminum foil packaged lunch box is formed by stamping a composite substrate in a mold. The composite substrate includes an inner contact layer, an aluminum foil core layer and a reinforcing layer from the inside to the outside. A first adhesive layer is provided between the inner contact layer and the aluminum foil core layer and between the aluminum foil core layer and the reinforcing layer.

[0026] The first adhesive layer is made of polyurethane resin and has a thickness of 3.5 μm.

[0027] The inner contact layer is made of polyethylene and has a thickness of 8 μm.

[0028] The reinforcing layer is formed by hydrogenated styrene-butadiene block copolymer, which is obtained by block polymerization of styrene monomer and butadiene monomer in a mass ratio of 28:72; the thickness of the reinforcing layer is 5.5 μm.

[0029] The aluminum foil core layer is formed by rolling and laminating three layers of aluminum foil. A second adhesive layer is provided between adjacent aluminum foil layers. The composition of the aluminum foil layers, by mass percentage, is: Si 0.08%, Fe 0.43%, Cu 0.15%, Mg 0.10%, Mn The composition is as follows: 0.01% Zn, 0.02% Zn, ≤0.02% of a single impurity element, with the balance being Al; the second adhesive layer is polyurethane resin; the thickness of the aluminum foil layer is 0.045 mm, the thickness of the second adhesive layer is 3.5 μm, and the thickness of the aluminum foil core layer is 0.12 mm; the preparation method of the aluminum foil core layer includes the following steps: weigh the corresponding raw materials according to the aluminum foil layer composition design, mix them, melt them at 750℃ for 40 min, add a refining agent at 750℃ and refine them for 20 min, cast and roll them at a speed of 900 mm / min (roller surface temperature is 90℃), and cold roll them at a speed of 6 m / min (roller surface temperature is 25℃) to obtain the aluminum foil layer; take 3 layers of aluminum foil, coat polyurethane resin between adjacent aluminum foil layers, and then perform calendering and composite (rolling temperature is 85℃, rolling pressure is 4.5 MPa, and rolling speed is 4.5 m / min) to obtain the aluminum foil core layer.

[0030] The method for manufacturing this aluminum foil-wrapped lunch box includes the following steps: Polyurethane resin is coated between the inner contact layer and the aluminum foil core layer, and between the aluminum foil core layer and the reinforcing layer. Then, it is placed in a mold with the bottom temperature of the mold controlled at 32°C and the side wall temperature of the mold controlled at 70°C. The composite substrate is stamped (the stamping pressure is 7MPa and the holding time is 12s), trimmed, and cleaned to obtain an aluminum foil packaged lunch box.

[0031] Example 3 An aluminum foil packaged lunch box is formed by stamping a composite substrate in a mold. The composite substrate includes an inner contact layer, an aluminum foil core layer and a reinforcing layer from the inside to the outside. A first adhesive layer is provided between the inner contact layer and the aluminum foil core layer and between the aluminum foil core layer and the reinforcing layer.

[0032] The first adhesive layer is made of polyurethane resin and has a thickness of 2.5 μm.

[0033] The inner contact layer is made of polyethylene and has a thickness of 6 μm.

[0034] The reinforcing layer is formed of hydrogenated styrene-butadiene block copolymer, which is obtained by block polymerization of styrene monomer and butadiene monomer in a mass ratio of 32:68; the thickness of the reinforcing layer is 5 μm. The aluminum foil core layer is formed by calendering and laminating three layers of aluminum foil, with a second adhesive layer between adjacent aluminum foil layers. The composition of the aluminum foil layers, by mass percentage, is: Si 0.12%, Fe 0.47%, Cu 0.18%, Mg 0.08%, Mn 0.03%, Zn The aluminum foil core layer has a thickness of 0.01% and a single impurity element ≤0.02%, with the balance being Al; the second adhesive layer is polyurethane resin; the aluminum foil layer has a thickness of 0.05 mm, the second adhesive layer has a thickness of 2.5 μm, and the aluminum foil core layer has a thickness of 0.14 mm; the preparation method of the aluminum foil core layer includes the following steps: weigh the corresponding raw materials according to the aluminum foil layer composition design, mix them, melt them at 750℃ for 40 min, add a refining agent at 750℃ for 20 min, cast and roll them at a speed of 900 mm / min (roller surface temperature is 90℃), and cold roll them at a speed of 6 m / min (roller surface temperature is 25℃) to obtain the aluminum foil layer; take 3 aluminum foil layers, coat polyurethane resin between adjacent aluminum foil layers, and then perform calendering and composite (rolling temperature is 95℃, rolling pressure is 4 MPa, and rolling speed is 5.5 m / min) to obtain the aluminum foil core layer.

[0035] The method for manufacturing this aluminum foil-wrapped lunch box includes the following steps: Polyurethane resin is coated between the inner contact layer and the aluminum foil core layer, and between the aluminum foil core layer and the reinforcing layer. Then, it is placed in a mold with the bottom temperature of the mold controlled at 38°C and the side wall temperature of the mold controlled at 75°C. The composite substrate is stamped (the stamping pressure is 9MPa and the holding time is 15s), trimmed, and cleaned to obtain an aluminum foil packaged lunch box.

[0036] Comparative Example 1 An aluminum foil-packaged lunch box differs from Example 1 in that: the aluminum foil core layer is formed by a single aluminum foil layer, without a second adhesive layer, eliminating the need for calendering and lamination, and the aluminum foil layer thickness is 0.10 mm. Everything else is the same as in Example 1.

[0037] Comparative Example 2 An aluminum foil-packaged lunch box differs from Example 1 in that no first or second adhesive layer is provided between the inner contact layer and the aluminum foil core layer, between the aluminum foil core layer and the reinforcing layer, or between adjacent aluminum foil layers; they are directly bonded together. Otherwise, it is the same as Example 1.

[0038] Comparative Example 3 An aluminum foil-wrapped lunch box differs from Example 1 in that the overall temperature of the mold is controlled at 50°C during stamping, without gradient temperature control at the bottom and sidewalls. Otherwise, it is the same as Example 1.

[0039] Comparative Example 4 An aluminum foil-wrapped lunch box differs from Example 1 in that the reinforcing layer is formed of polyethylene. Otherwise, it is the same as Example 1.

[0040] Comparative Example 5 An aluminum foil-packaged lunch box differs from Example 1 in that the composition of the aluminum foil layer, by mass percentage, is: Si 0.03%, Fe 0.35%, Cu 0.10%, Mg 0.05%, Mn 0.06%, Zn 0.06%, with individual impurity elements ≤0.04%, and the balance being Al. Everything else is the same as in Example 1.

[0041] Performance testing The aluminum foil packaging lunch boxes prepared in the examples and comparative examples were tested for tensile strength, compressive deformation, interlayer peel strength, leakage rate, wall thickness uniformity, and impact strength. The tensile strength test was conducted according to GB / T 228.1-2010; the compressive deformation test was conducted according to GB / T 32088-2015; and the interlayer peel strength test was conducted according to GB / T The test was conducted according to GB / T 10004-2011. The leakage rate test involved filling the aluminum foil-wrapped food container with 50ml of simulated broth (water + 2% starch) and simulating the food's bumpy ride for 30 minutes (frequency 5Hz, amplitude 10mm). The total weight of the aluminum foil-wrapped food container and broth before and after the test was recorded, and the leakage rate was calculated as: Leakage rate = (Total weight of aluminum foil-wrapped food container and broth before test - Total weight of aluminum foil-wrapped food container and broth after test) / Total weight of aluminum foil-wrapped food container and broth before test × 100%. The wall thickness uniformity test involved measuring five points on the bottom and five points on the sidewalls of the aluminum foil-wrapped food container using a thickness gauge and calculating the maximum difference. The impact strength test was conducted according to GB / T 10004-2008. The test results are shown in Table 1.

[0042] Table 1 Referring to the data in Table 1, compared with Example 1, although the thickness of the single-layer aluminum foil is the same as that of the three-layer composite aluminum foil core layer, the test results show that its overall performance is significantly inferior to that of the other examples. Example 1, thanks to the synergistic stress effect between the multiple aluminum foil layers and the tight bonding brought by the second adhesive layer, exhibits significant advantages in tensile strength, compressive deformation resistance, and impact resistance. In contrast, Comparative Example 1, lacking a structural design for dispersing interlayer stress, is prone to local deformation or even breakage under external forces, ultimately leading to a significant increase in leakage rate. This fully demonstrates that the multi-layer composite aluminum foil core layer is the key to improving the structural stability of the lunchbox.

[0043] Comparative Example 2 eliminated all interlayer adhesive layers, relying solely on the bonding of the materials themselves. Its interlayer peel strength was significantly lower than that of the embodiments, only about 1 / 8 of that of Example 1. Without the connecting effect of adhesive layers, the structural layers cannot form a unified load-bearing structure, making them prone to interlayer separation under stress. This not only leads to a decrease in tensile and impact resistance but also compromises the sealing integrity of the food container, resulting in a substantial increase in leakage rate. In contrast, the embodiments achieved a strong bond between the layers through the precise matching of the first and second adhesive layers, ensuring a synergistic improvement in mechanical properties and sealing performance, highlighting the core connecting value of adhesive layers in composite substrates.

[0044] Comparative Example 3 used overall constant temperature stamping instead of the gradient temperature-controlled stamping of the Examples. The overall temperature of the mold was 50°C, resulting in a significant deterioration in the uniformity of its wall thickness, with the maximum difference exceeding that of Example 1 by more than double. The Examples, through a gradient design that prevents excessive material thinning at the bottom of the mold and promotes uniform material flow with moderate heating of the side walls, ensured consistent wall thickness and balanced structural stress after the lunchbox was formed. In contrast, Comparative Example 3, due to improper temperature control, experienced uneven material flow during molding, resulting in weak local areas. Under external impact and extrusion, it was prone to deformation and leakage, with higher leakage rate and compressive deformation than the Examples. This verifies the important significance of gradient temperature-controlled molding technology in improving the molding quality and performance of lunchboxes.

[0045] In Comparative Example 4, when polyethylene was used instead of the hydrogenated styrene-butadiene block copolymer in the examples as the reinforcing layer, its impact strength and compressive deformation resistance were significantly inferior to those of the examples. The hydrogenated styrene-butadiene block copolymer possesses excellent elasticity and impact resistance, which complements the rigidity of the aluminum foil core layer, effectively absorbing external impact energy and reducing food container deformation. In contrast, polyethylene lacks sufficient elasticity and impact resistance, failing to provide effective protection for the aluminum foil core layer. This resulted in a significantly higher leakage rate in the simulated takeout bump test, fully demonstrating the crucial influence of the material selection for the reinforcing layer and the performance compatibility with the aluminum foil core layer on the overall deformation resistance and leak-proof capability of the food container.

[0046] The aluminum foil layer composition of Comparative Example 5 deviated from the scope defined in this invention, with lower content of some alloying elements and higher content of impurity elements, resulting in lower tensile strength and impact strength compared to the embodiments. The aluminum foil composition defined in this invention, through the precise ratio of elements such as Si, Fe, Cu, and Mg, can form a stable reinforcing phase, improving the mechanical properties of the aluminum foil itself and providing reliable support for the aluminum foil core layer. In contrast, Comparative Example 5, due to improper component ratio, had insufficient aluminum foil strength and could not effectively disperse external forces, leading to increased compressive deformation and leakage rate in the lunchbox. The comparative results demonstrate that the aluminum foil layer composition defined in this invention is fundamental to ensuring the core strength of the lunchbox.

[0047] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. An aluminum foil-packaged lunch box, characterized in that, The aluminum foil packaging lunch box is formed by stamping a composite substrate in a mold. The composite substrate includes an inner contact layer, an aluminum foil core layer and a reinforcing layer from the inside to the outside. A first adhesive layer is provided between the inner contact layer and the aluminum foil core layer and between the aluminum foil core layer and the reinforcing layer. The inner contact layer is formed of polyethylene; The reinforcing layer is formed of a hydrogenated styrene-butadiene block copolymer; The aluminum foil core layer is formed by rolling and laminating at least three layers of aluminum foil, with a second adhesive layer between adjacent aluminum foil layers. The composition of the aluminum foil layers, by mass percentage, is: Si 0.05%-0.15%, Fe 0.40%-0.50%, Cu 0.12%-0.20%, Mg 0.08%-0.10%, Mn ≤0.05%, Zn ≤0.05%, single impurity element ≤0.03%, and the balance being Al. Both the first adhesive layer and the second adhesive layer are polyurethane resins.

2. The aluminum foil packaged lunch box according to claim 1, characterized in that, The composition of the aluminum foil layer by mass percentage is as follows: Si 0.08%-0.12%, Fe 0.43%-0.47%, Cu 0.15%-0.18%, Mg 0.09%-0.10%, Mn ≤0.03%, Zn ≤0.03%, single impurity element ≤0.02%, and the balance is Al with a mass percentage of Al ≥99.2%.

3. The aluminum foil packaged lunch box according to claim 1, characterized in that, The thickness of the aluminum foil layer is 0.03mm-0.05mm, the thickness of the second adhesive layer is 2μm-4μm, and the thickness of the aluminum foil core layer is 0.09mm-0.15mm.

4. The aluminum foil packaged lunch box according to claim 1, characterized in that, The method for preparing the aluminum foil core layer includes the following steps: According to the aluminum foil layer composition design, weigh the corresponding raw materials, mix, melt, refine, cast, and cold roll to obtain the aluminum foil layer; Take at least 3 layers of the aluminum foil, coat the polyurethane resin between adjacent aluminum foil layers, and then perform the calendering and lamination to obtain the aluminum foil core layer; The rolling temperature of the calendered composite is 80℃-100℃, and the rolling pressure is 3MPa-5MPa.

5. The aluminum foil packaged lunch box according to claim 1, characterized in that, The hydrogenated styrene-butadiene block copolymer is obtained by block polymerization of styrene monomer and butadiene monomer in a mass ratio of (25-35):(65-75).

6. The aluminum foil packaged lunch box according to claim 1, characterized in that, The thickness of the inner contact layer is 6μm-8μm, the thickness of the reinforcing layer is 5μm-6μm, and the thickness of the first adhesive layer is 2μm-4μm.

7. The method for manufacturing an aluminum foil-packaged lunch box as described in any one of claims 1-6, characterized in that, Includes the following steps: The polyurethane resin is coated between the inner contact layer and the aluminum foil core layer, and between the aluminum foil core layer and the reinforcing layer. Then, the substrate is placed in the mold, the bottom temperature of which is controlled at 30℃-40℃ and the side wall temperature of which is controlled at 60℃-80℃. The composite substrate is then stamped, trimmed, and cleaned to obtain the aluminum foil packaging lunch box.

8. The method for manufacturing an aluminum foil-packaged lunch box according to claim 7, characterized in that, The stamping pressure is 6MPa-10MPa, and the holding time is 10s-18s.

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