Aluminum foil bag for food packaging and process for preparing the same

Abstract

The application relates to the technical field of food packaging materials, and particularly discloses an aluminum foil bag for food packaging and a preparation process thereof. The aluminum foil bag comprises an outer layer, an aluminum foil layer and an inner layer which are sequentially stacked from outside to inside, and the inner layer is an anti-puncture heat-seal layer which is made of a composite material containing polybutylene succinate, polycaprolactone, ethylene-vinyl acetate copolymer and nano-silicon dioxide. The preparation process comprises the steps of raw material mixing, melt blending and granulation, casting film forming, dry compounding and bag making. Through the synergistic effect of the components, the aluminum foil bag can keep good heat-seal performance and biodegradability, and the puncture resistance and barrier performance are significantly improved, the problem that traditional aluminum foil bags are broken and puncture the inner layer to cause sand eye gas leakage due to wrinkles is effectively solved, and the aluminum foil bag has both use reliability and environmental protection benefits.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials technology, specifically relating to an aluminum foil bag for food packaging and its preparation process. Background Technology

[0002] In the food packaging industry, aluminum foil composite bags are widely used for products requiring long-term preservation due to their excellent barrier properties, especially for vacuum packaging of ingredients containing hard, angular components such as hot pot, dried goods, and bone broth. The core requirement for this type of packaging is that it must remain intact and sealed after being vacuum-sealed and subjected to the vibrations and compression of long-distance transportation to ensure that the contents do not deteriorate within the shelf life.

[0003] In practical applications, it has been found that when conventional aluminum foil bags are used to package such rigid contents, the sharp edges and creases of the food inside can easily cause very small perforations in the packaging, resulting in the failure of the internal vacuum environment.

[0004] Firstly, during transport, the sharp creases created by hard objects cause continuous, minute bending, much like repeatedly folding a metal wire. After dozens to hundreds of such bends, existing aluminum foil materials develop micro-cracks at the crease tips due to stress concentration. Once the foil cracks, its barrier function is lost. Secondly, when the outer aluminum foil breaks, the break becomes quite sharp. Under the combined effect of negative pressure inside the bag and external compression, the broken foil exerts extremely high pressure on the inner plastic film. Commonly used inner layer materials (such as polyethylene or traditional polylactic acid) are relatively uniform and soft, designed to resist uniform tensile force, but they cannot effectively disperse concentrated point stress, making them very easy to puncture, forming pinholes connecting the inside and outside.

[0005] Ultimately, this directly leads to the loss of the packaging bag's air-barrier and moisture-proof functions, making the food inside the packaging prone to oxidation and spoilage, thus posing a food safety hazard. Summary of the Invention

[0006] The purpose of this invention is to provide an aluminum foil bag for food packaging and its manufacturing process, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, according to one aspect of the present invention, an aluminum foil bag for food packaging is provided, comprising an outer layer, an aluminum foil layer, and an inner layer stacked sequentially from the outside to the inside, characterized in that the inner layer is a puncture-resistant heat-sealing layer made of a composite material comprising the following components in parts by weight: 65-85 parts polybutylene succinate; 10-25 parts polycaprolactone; 5-12 parts ethylene-vinyl acetate copolymer; and 1-5 parts nano-silica.

[0008] Preferably, the inner composite material further comprises 0.3-1.0 parts of antioxidant 1010 and 0.5-2.0 parts of calcium stearate.

[0009] Preferably, the nano-silica is nano-silica with a surface modified by a silane coupling agent, and its particle size ranges from 20 to 60 nm.

[0010] Preferably, the outer layer is a polyethylene terephthalate film or a biaxially oriented polyamide film with a thickness of 12-25 μm; the aluminum foil layer has a thickness of 7-9 μm; and the inner layer has a thickness of 50-80 μm.

[0011] According to another aspect of the present invention, a process for preparing aluminum foil bags for food packaging is provided, comprising the following steps: S1. Mixing the components according to the formula using a high-speed mixer to obtain a premix;

[0012] S2. The premixed material is fed into a twin-screw extruder, and after melt blending and extrusion granulation, inner layer composite material particles are obtained; wherein, the extruder processing temperature is 150-180℃;

[0013] S3. The inner layer composite material particles are cast into a film using a casting extruder to form an inner layer film;

[0014] S4. The outer film, aluminum foil layer and inner film are laminated using a dry laminator, water-based polyurethane adhesive is used, and the composite film is obtained after drying and curing.

[0015] S5. The composite film is cut and heat-sealed into aluminum foil bags using a bag-making machine.

[0016] Preferably, the length-to-diameter ratio of the twin-screw extruder in step S2 is 40:1 to 48:1, and the screw speed is 200-300 rpm.

[0017] Preferably, during the casting process in step S3, the temperature of the cooling roller is controlled at 25-35℃.

[0018] Preferably, the curing process in step S4 is carried out at 45-55°C for 36-60 hours.

[0019] The aluminum foil bag for food packaging produced by this invention can be used to package food contents with hard edges.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] By combining a specific ratio of polycaprolactone, ethylene-vinyl acetate copolymer, and nano-silica in the inner layer material, polycaprolactone, as a flexible component, can form dispersed particles in the matrix and absorb impact energy through its own deformation; ethylene-vinyl acetate copolymer, as an elastic component, can effectively hinder the propagation of microcracks; and nano-silica, as rigid particles, can deflect and disperse local stress. These three components produce a synergistic toughening effect, enabling the inner layer of the aluminum foil bag to effectively resist punctures from sharp points formed by aluminum foil breakage when packaging rigid, angular contents, thereby reducing the risk of air leakage.

[0022] By using polybutylene succinate as the continuous phase matrix and controlling the addition ratio of polycaprolactone and ethylene-vinyl acetate copolymer, the aluminum foil bag achieves significantly enhanced puncture resistance while maintaining good heat-sealing properties in its inner layer. This balances the various properties of the inner layer materials, ensuring reliable packaging sealing. The good compatibility between the components ensures the stability of the inner layer material processing, while the biodegradability of the main material is maintained, allowing the aluminum foil bag to meet both performance and environmental requirements.

[0023] By introducing nano-silica and antioxidants into the inner layer material, the uniform dispersion of nano-silica in the polymer matrix effectively extends the permeation path of gas molecules within the material, thereby assisting the aluminum foil layer in enhancing the overall barrier performance of the packaging. Simultaneously, the addition of antioxidants effectively inhibits the thermo-oxidative aging of the inner layer material during processing and subsequent use, ensuring the performance stability of the aluminum foil bag during storage and distribution.

[0024] By selecting biodegradable polybutylene succinate and polycaprolactone as the main materials for the inner layer, and combining them with environmentally friendly adhesives, the final aluminum foil bag has both practical function and environmental benefits. Attached Figure Description

[0025] Figure 1 This is a SEM image of the brittle fracture surface of the inner thin film in Embodiment 1 of the present invention;

[0026] Figure 2 This is a SEM image of the brittle fracture surface of the inner thin film of Comparative Example 3 of the present invention. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] In the claims and description of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0029] Figure 1 The image shown is a scanning electron microscope (SEM) image of the brittle fracture surface of the inner composite material obtained in Embodiment 1 of the present invention. The acquisition method is as follows: the sample with the brittle fracture surface facing upwards is fixed on the sample stage and placed in a high vacuum environment. Scanning is performed using a 15kV accelerating voltage and secondary electron (SE) imaging mode, with a working distance of approximately 8mm. The image resolution is set to 1μm, clearly showing the uniform dispersion of nano-silica particles (bright white spots) in the PBS matrix and the morphological characteristics of the fracture surface toughness.

[0030] Figure 2 This is a scanning electron microscope (SEM) image of the brittle fracture surface of the inner layer composite material obtained in Comparative Example 3 of this invention. The acquisition parameters are the same as those of the original image. Figure 1 Identical to all: high vacuum environment, 15kV accelerating voltage, secondary electron mode, and 8mm working distance. The image resolution is also 1μm, showing the relatively smooth and uniform plastic fracture morphology of the matrix after the absence of nano-silica components.

[0031] This invention relates to an aluminum foil bag for food packaging, comprising an outer layer, an aluminum foil layer, and an inner layer stacked sequentially from the outside to the inside. The inner layer is a puncture-resistant heat-sealing layer made of a composite material comprising the following components in parts by weight: 65-85 parts polybutylene succinate; 10-25 parts polycaprolactone; 5-12 parts ethylene-vinyl acetate copolymer; and 1-5 parts nano-silica.

[0032] Polybutylene succinate is used as the matrix resin in an amount of 65-85 parts, forming the continuous phase of the material. This dosage range ensures that the material has the necessary mechanical strength, biodegradability, and basic thermal adhesion as a heat-sealing layer.

[0033] Polycaprolactone and ethylene-vinyl acetate copolymer were used as a composite toughening system, with dosages of 10-25 parts and 5-12 parts, respectively. Polycaprolactone is a flexible, biodegradable polyester, and its introduction aims to improve the material's flexibility and impact resistance by forming a dispersed phase. The ethylene-vinyl acetate copolymer, as an elastomer phase, further inhibits crack propagation. At this ratio, both components synergistically work with the matrix resin to construct a multi-layered energy dissipation mechanism, which is the structural basis for the high puncture resistance of the inner layer.

[0034] The amount of nano-silica used is 1-5 parts. As a nano-reinforcing filler, its surface is usually modified with a silane coupling agent. This treatment aims to improve its interfacial compatibility and dispersion stability in the hydrophobic polymer matrix. The introduction of nanoparticles can act as stress concentration points at the nanoscale, inducing plastic deformation of the matrix and effectively pinning cracks, thereby synergistically improving the rigidity, barrier properties, and puncture resistance of the material.

[0035] Through the specific combination and synergy of the above components, the inner layer successfully achieves an optimized balance between puncture resistance and heat-sealing properties. Its puncture resistance is significantly improved to meet the requirements of packaging rigid contents; at the same time, its heat-sealing strength is maintained at a high level, ensuring the sealing reliability of the packaging bag.

[0036] The inner composite material also contains 0.3-1.0 parts of antioxidant 1010 and 0.5-2.0 parts of calcium stearate. The addition of antioxidant 1010 aims to inhibit thermo-oxidative aging of the polymer during high-temperature processing and use, ensuring the long-term stability of the material. Calcium stearate, as a lubricant, is mainly used to improve the flowability and release properties of the material in processing equipment.

[0037] In terms of structural design, the outer layer uses a polyethylene terephthalate film or biaxially oriented polyamide film with a thickness of 12-25 μm, primarily providing excellent mechanical strength and printability. The aluminum foil layer, with a thickness of 7-9 μm, serves as the core barrier layer, effectively blocking oxygen, water vapor, and light. The inner layer has a thickness of 50-80 μm; this thickness range ensures sufficient mechanical strength and sealing reliability while also considering material flexibility, cost, and processing efficiency.

[0038] A manufacturing process for aluminum foil bags used in food packaging includes the following steps:

[0039] S1. Mix the components according to the formula using a high-speed mixer to obtain a premix;

[0040] S2. The premixed material is fed into a twin-screw extruder, and after melt blending and extrusion granulation, inner layer composite material particles are obtained; wherein, the extruder processing temperature is 150-180℃;

[0041] S3. The inner layer composite material particles are cast into a film using a casting extruder to form an inner layer film;

[0042] S4. The outer film, aluminum foil layer and inner film are laminated using a dry laminator, water-based polyurethane adhesive is used, and the composite film is obtained after drying and curing.

[0043] S5. The composite film is cut and heat-sealed into aluminum foil bags using a bag-making machine.

[0044] Detailed explanation of step S1:

[0045] This step aims to achieve preliminary homogeneous mixing of the components on a macroscopic scale, laying the foundation for subsequent melt blending. The physical state of the raw materials and the mixing process have a decisive influence on the homogeneity of the premix.

[0046] Polybutylene succinate (PBS), polycaprolactone (PCL), and ethylene-vinyl acetate copolymer (EVA) are all used in particulate form. Nano-silica is in powder form, with its surface modified by a silane coupling agent. This pretreatment is intended to improve the compatibility and dispersion stability of the nanoparticles with the polymer matrix during subsequent melt processing.

[0047] To achieve thorough mixing, the speed of the high-speed mixer is controlled at 300 to 500 rpm, and the mixing time lasts for 5 to 10 minutes. During this process, antioxidant 1010 and a small amount of additives such as calcium stearate are uniformly adhered to the surface of the polymer particles and initially interpenetrate with the nano-silica powder to form a premix with a uniform appearance.

[0048] Detailed explanation of step S2:

[0049] This step is crucial for achieving nanoscale dispersion and synergistic toughening of multiphase systems. Through melt blending and shearing, the components achieve uniform microscale dispersion and interfacial bonding in the molten state.

[0050] To achieve this, the temperature range from the feed port to the die in the twin-screw extruder is set to 150°C to 180°C. This temperature range is designed to ensure that polymer components such as PBS, PCL, and EVA can be fully melted while avoiding thermal degradation due to excessively high temperatures.

[0051] To achieve effective shear dispersion, the extruder screw speed is set to 200 to 300 rpm. The twin-screw extruder used has an aspect ratio of 40:1 to 48:1. The relatively long aspect ratio ensures that the material has sufficient residence time in the barrel and undergoes sufficient shearing. During this process, the nano-silica agglomerates are effectively broken up and uniformly distributed in the continuous phase of the polymer melt as nanoscale particles.

[0052] Detailed explanation of step S3:

[0053] The goal of this step is to mold the composite material particles into a film with uniform thickness and a smooth surface. The temperature of the cast extruder from the feed section to the die is controlled within the range of 150-180℃ to ensure good plasticization and flow stability of the material during the extrusion process.

[0054] The melt immediately contacts and solidifies upon extrusion from the die and onto the cooling roller. The temperature of the cooling roller is controlled between 25°C and 35°C. This temperature range is set based on the control of polymer crystallization behavior: below 25°C, excessively rapid cooling may lead to incomplete crystallization; above 35°C, excessively slow cooling will result in overly large spherulite structures, affecting the mechanical properties of the film. Within this temperature range, the polymer can form a suitable crystalline structure, which is beneficial for the film to obtain good overall performance.

[0055] Detailed explanation of step S4:

[0056] This step uses a dry lamination process to firmly bond the outer layer, aluminum foil layer, and inner film. A water-based polyurethane adhesive is used in the lamination process. After the adhesive is evenly applied to the film surface using an anilox roller, the film enters an oven for drying. The oven temperature is controlled between 50°C and 60°C to ensure sufficient moisture evaporation.

[0057] After initial drying and lamination, the roll material undergoes a curing treatment. The curing process is carried out at a temperature of 45°C to 55°C for 36 to 60 hours. Under these conditions, the waterborne polyurethane adhesive completes full cross-linking and curing, achieving a strong bond between the layers.

[0058] Detailed explanation of step S5:

[0059] This step completes the final shaping of the aluminum foil bag, achieving a reliable seal through precise control of the heat-sealing process parameters. The bag-making process is completed on a fully automated bag-making machine, and the composite film enters the heat-sealing process after being slit.

[0060] The heat-sealing temperature is controlled at 130-150℃, the heat-sealing pressure is 0.2-0.5MPa, and the heat-sealing time is maintained at 1-2 seconds. This combination of parameters ensures full fusion of the inner layer material at the interface, forming a dense sealing area, while preventing damage to the material structure from excessive temperature or pressure. After heat sealing, the bag is cooled and shaped, ultimately producing an aluminum foil packaging bag with good sealing performance.

[0061] Example 1:

[0062] (1) Raw material premix (S1): 65 parts by weight of polybutylene succinate (PBS) particles, 25 parts by weight of polycaprolactone (PCL) particles, 5 parts by weight of ethylene-vinyl acetate copolymer (EVA) particles, 3 parts by weight of nano-silica with surface modified by silane coupling agent, 0.8 parts by weight of antioxidant 1010 and 1.2 parts by weight of calcium stearate were put into a high-speed mixer; the mixture was mixed at a speed of 400 rpm for 8 minutes to obtain a premix with a uniform appearance.

[0063] (2) Melt blending and granulation (S2): The premixed material is fed into a co-rotating twin-screw extruder. The temperature zones of the extruder from the feed port to the die are set as follows: Zone 1 155℃, Zone 2 160℃, Zone 3 165℃, Zone 4 170℃, Zone 5 172℃, and Zone 6 175℃. The die temperature is controlled at 172℃. The screw speed is set to 280 rpm, and the length-to-diameter ratio is 44:1. The melt is water-cooled and then pelletized to obtain inner layer composite material particles.

[0064] (3) Casting film (S3): The above composite material particles are formed into a film by a single screw casting extruder; the temperature of each zone of the casting machine is set as follows: Zone 1 162℃, Zone 2 168℃, Zone 3 172℃, Zone 4 176℃, and the die head temperature is 174℃; after the melt is extruded from the T-die, it comes into contact with the cooling roller with the surface temperature controlled at 30℃ and solidifies, and is pulled and wound up to form an inner layer film with a thickness of 60μm.

[0065] (4) Dry lamination and curing (S4): A 12μm thick biaxially oriented polyamide (BOPA) film is selected as the outer layer and a 7μm aluminum foil as the barrier layer. A water-based polyurethane adhesive is used to laminate the BOPA outer film with the aluminum foil layer and the aluminum foil layer with the inner film in sequence through a dry lamination machine. The laminated material is dried in a 55℃ drying tunnel and then the roll is transferred to a 50℃ curing chamber for 48 hours.

[0066] (5) Bag making process (S5): The cured composite film is cut to the predetermined width by a slitting machine, and then aluminum foil bags are made on a three-side sealing fully automatic bag making machine; the heat sealing knife temperature is set to 140℃, the heat sealing pressure is 0.3MPa, and the heat sealing time is 1.2 seconds; after bag making, the final product is obtained through inspection and packaging.

[0067] Example 2:

[0068] (1) Add 85 parts by weight of PBS particles, 10 parts by weight of PCL particles, 12 parts by weight of EVA particles, 1 part by weight of nano-silica, 0.3 parts by weight of antioxidant 1010 and 0.5 parts by weight of calcium stearate to a high-speed mixer. Mix at 350 rpm for 10 minutes to obtain a premix.

[0069] (2) The premixed material is fed into a twin-screw extruder, and the temperature zones are set as follows: Zone 1 150℃, Zone 2 158℃, Zone 3 162℃, Zone 4 168℃, Zone 5 170℃, Zone 6 175℃, and the die temperature is 170℃. The screw speed is adjusted to 220 rpm, and the length-to-diameter ratio is 40:1. After melt blending and water cooling pelletizing, composite material particles are obtained.

[0070] (3) The granules were formed into a film with a thickness of 50 μm using a cast extruder. The temperatures of each zone were set as follows: Zone 1 160℃, Zone 2 165℃, Zone 3 170℃, Zone 4 174℃, and the die temperature was 172℃. The temperature of the cooling roller was controlled at 25℃, and the inner layer film was obtained by traction and winding.

[0071] (4) A 25μm thick polyethylene terephthalate (PET) film was selected as the outer layer, and a 9μm aluminum foil was selected as the barrier layer. The same water-based polyurethane adhesive was used to complete the interlayer bonding through a two-stage lamination process. After the laminated roll was dried in a 60℃ oven, it was cured at 45℃ for 60 hours.

[0072] (5) After the composite film is cut, it is made into bags on a bag making machine at a heat sealing temperature of 135℃, a heat sealing pressure of 0.5MPa, and a heat sealing time of 1.5 seconds. After quality inspection, the bags are put into storage.

[0073] Example 3:

[0074] (1) Add 80 parts by weight of PBS particles, 12 parts by weight of PCL particles, 10 parts by weight of EVA particles, 4 parts by weight of nano-silica, 0.5 parts by weight of antioxidant 1010 and 1.0 parts by weight of calcium stearate to a high-speed mixer. Mix at 380 rpm for 9 minutes to obtain a premix.

[0075] (2) The premixed material is fed into a twin-screw extruder, and the temperature zones are set as follows: Zone 1 152℃, Zone 2 162℃, Zone 3 166℃, Zone 4 170℃, Zone 5 173℃, Zone 6 177℃, and the die temperature is 173℃. The screw speed is adjusted to 250 rpm, and the length-to-diameter ratio is 42:1. After melt blending and water cooling pelletizing, composite material particles are obtained.

[0076] (3) The granules were formed into a film with a thickness of 55 μm using a cast extruder. The temperatures of each zone were set as follows: Zone 1 161℃, Zone 2 167℃, Zone 3 171℃, Zone 4 175℃, and the die temperature was 173℃. The temperature of the cooling roller was controlled at 28℃, and the inner layer film was obtained by traction and winding.

[0077] Steps (4) to (5) are exactly the same as in Example 1.

[0078] Example 4:

[0079] (1) 75 parts by weight of PBS particles, 15 parts by weight of PCL particles, 8 parts by weight of EVA particles, 5 parts by weight of nano-silica, 0.6 parts by weight of antioxidant 1010 and 0.8 parts by weight of calcium stearate were added to a high-speed mixer. The mixture was mixed at 420 rpm for 7 minutes to obtain a premix.

[0080] (2) The premixed material is fed into a twin-screw extruder, and the temperature zones are set as follows: Zone 1 158℃, Zone 2 163℃, Zone 3 168℃, Zone 4 172℃, Zone 5 175℃, Zone 6 178℃, and the die temperature is 175℃. The screw speed is adjusted to 270 rpm, and the length-to-diameter ratio is 46:1. After melt blending and water cooling pelletizing, composite material particles are obtained.

[0081] (3) The granules were formed into a film with a thickness of 65 μm using a cast extruder. The temperatures of each zone were set as follows: Zone 1 163℃, Zone 2 169℃, Zone 3 173℃, Zone 4 177℃, and the die temperature was 175℃. The cooling roller temperature was controlled at 32℃, and the inner layer film was obtained by traction and winding.

[0082] Steps (4) to (5) are exactly the same as in Example 1.

[0083] Example 5:

[0084] Steps (1) to (3) are exactly the same as in Example 1.

[0085] (4) A 18μm thick polyethylene terephthalate (PET) film was selected as the outer layer, and an 8μm aluminum foil was selected as the barrier layer. Water-based polyurethane adhesive was used to complete the interlayer bonding through a two-stage lamination process. After the laminated roll was dried in a 58℃ oven, it was cured at 52℃ for 42 hours.

[0086] (5) After the composite film is cut, it is made into bags on a bag making machine at a heat sealing temperature of 145℃, a heat sealing pressure of 0.4MPa, and a heat sealing time of 1.0 seconds. After quality inspection, the bags are put into storage.

[0087] Comparative Example 1:

[0088] (1) No specific inner layer material is prepared; commercially available 60μm thick cast polypropylene (CPP) film is used directly as the inner layer of the aluminum foil bag.

[0089] Steps (2) to (3) are exactly the same as in Example 1.

[0090] (4) A 12 μm thick biaxially oriented polyamide (BOPA) film was selected as the outer layer, a 7 μm thick aluminum foil as the barrier layer, and a 60 μm thick CPP film as the inner layer. The same water-based polyurethane adhesive and composite process as in Example 1 were used. After drying in a 55°C oven, the film was cured at 50°C for 48 hours.

[0091] (5) The steps are exactly the same as in Example 1.

[0092] Comparative Example 2:

[0093] (1) Add 83 parts by weight of PBS particles, 15 parts by weight of PCL particles, 0.5 parts by weight of antioxidant 1010 and 1.5 parts by weight of calcium stearate to a high-speed mixer. Mix at 400 rpm for 8 minutes to obtain a premix.

[0094] (2) The premixed material is fed into a twin-screw extruder, and the temperature zones are set as follows: Zone 1 155℃, Zone 2 160℃, Zone 3 165℃, Zone 4 170℃, Zone 5 172℃, Zone 6 175℃, and the die temperature is 172℃. The screw speed is set to 280 rpm, and the length-to-diameter ratio is 44:1. The melt is water-cooled and pelletized to obtain composite material particles.

[0095] (3) The granules were formed into a film with a thickness of 60 μm using a cast extruder. The temperatures of each zone were set as follows: Zone 1 162℃, Zone 2 168℃, Zone 3 172℃, Zone 4 176℃, and the die temperature was 174℃. The temperature of the cooling roller was controlled at 30℃ to obtain the inner layer film.

[0096] Steps (4) to (5) are exactly the same as in Example 1.

[0097] Comparative Example 3:

[0098] (1) 78 parts by weight of PBS particles, 15 parts by weight of PCL particles, 8 parts by weight of EVA particles, 0.5 parts by weight of antioxidant 1010 and 1.0 parts by weight of calcium stearate were added to a high-speed mixer. The mixture was mixed at 400 rpm for 8 minutes to obtain a premix.

[0099] (2) The premixed material is fed into a twin-screw extruder, and the temperature zones are set as follows: Zone 1 155℃, Zone 2 160℃, Zone 3 165℃, Zone 4 170℃, Zone 5 172℃, Zone 6 175℃, and the die temperature is 172℃. The screw speed is set to 280 rpm, and the length-to-diameter ratio is 44:1. The melt is water-cooled and pelletized to obtain composite material particles.

[0100] (3) The granules were formed into a film with a thickness of 60 μm using a cast extruder. The temperatures of each zone were set as follows: Zone 1 162℃, Zone 2 168℃, Zone 3 172℃, Zone 4 176℃, and the die temperature was 174℃. The temperature of the cooling roller was controlled at 30℃ to obtain the inner layer film.

[0101] Steps (4) to (5) are exactly the same as in Example 1.

[0102] Comparative Example 4:

[0103] (1) 60 parts by weight of PBS particles, 25 parts by weight of PCL particles, 12 parts by weight of EVA particles, 3 parts by weight of nano-silica, 0.5 parts by weight of antioxidant 1010 and 1.0 part of calcium stearate were added to a high-speed mixer. The mixture was mixed at 400 rpm for 8 minutes to obtain a premix.

[0104] (2) The premixed material is fed into a twin-screw extruder, and the temperature zones are set as follows: Zone 1 155℃, Zone 2 160℃, Zone 3 165℃, Zone 4 170℃, Zone 5 172℃, Zone 6 175℃, and the die temperature is 172℃. The screw speed is set to 280 rpm, and the length-to-diameter ratio is 44:1. The melt is water-cooled and pelletized to obtain composite material particles.

[0105] (3) The granules were formed into a film with a thickness of 60 μm using a cast extruder. The temperatures of each zone were set as follows: Zone 1 162℃, Zone 2 168℃, Zone 3 172℃, Zone 4 176℃, and the die temperature was 174℃. The temperature of the cooling roller was controlled at 30℃ to obtain the inner layer film.

[0106] Steps (4) to (5) are exactly the same as in Example 1.

[0107] The aluminum foil bag samples obtained from the examples and comparative examples were subjected to performance tests. All performance parameters were tested according to the relevant Chinese national standards (GB / T) or international standards, as detailed below:

[0108] Composite structure puncture resistance test: To simulate the actual failure mode of aluminum foil bags when packaging rigid, angular contents, a custom puncture test method was adopted. During the test, a standard cut was first made in the aluminum foil layer of the composite film sample to simulate wrinkle breakage. Then, referring to the puncture resistance test principles in GB / T21302-2007 "General Rules for Composite Films and Bags for Packaging", a 1.0 mm diameter puncture probe was used to puncture the sample at a speed of 50 mm / min, and the maximum puncture force (unit: N) was recorded. This force value directly characterizes the overall ability of the packaging to resist the inner layer being punctured due to the breakage of the aluminum foil layer.

[0109] Puncture resistance test of the inner film: To characterize the puncture resistance of the inner layer material independently, the pure inner film is separated from the composite structure as a sample and tested according to the puncture resistance test method specified in GB / T21302-2007 "General Rules for Composite Films and Bags for Packaging". A standard puncture probe is used to test under the same conditions, and the maximum force (unit: N) at which the film ruptures is recorded. This indicator directly reflects the inner layer material's ability to resist puncture by localized sharp stress.

[0110] Biodegradability Testing: To verify the environmentally friendly characteristics of the material, pure inner layer film samples were tested according to GB / T19277.1-2011 "Determination of the final aerobic biodegradability of materials under controlled composting conditions by method for determining the release of carbon dioxide". In a specified composting environment, the biodegradability (%) of the samples was measured over 180 days to scientifically evaluate its biodegradability and confirm that it meets the requirements for green packaging materials.

[0111] Barrier performance test: To evaluate the packaging's ability to block oxygen and water vapor, the oxygen permeability was tested according to GB / T19789-2005 "Packaging Materials - Plastic Films and Sheets - Oxygen Permeability Test - Coulometric Method", with the unit being cm. 3 / (m 2 The water vapor transmission rate is expressed as g / (m·atm). It is also tested according to GB / T21529-2008 "Test Method for Water Vapor Permeability of Plastic Films and Sheets - Electrolytic Sensor Detection Method", with units of g / (m·atm). 2 •d) indicates that the test sample is a composite film with an intact structure, and the test was conducted under a standard environment of 23±1℃ and 50±5% relative humidity. These two indicators directly reflect the packaging's ability to prevent the contents from oxidizing, deteriorating, and becoming damp.

[0112] The performance of the above aluminum foil bag samples was tested, and the results are summarized in the table below:

[0113]

[0114] Based on the above test results, it can be found that in the composite structure puncture resistance test, all embodiments of the present invention exhibit superior resistance compared to traditional structures, with puncture force values ​​ranging from 13.8N to 14.9N. Embodiment 1 measured 14.2N, and Embodiment 4 reached the highest at 14.9N. These figures are significantly higher than the 10.5N of the traditional CPP structure in Comparative Example 1, representing an improvement of approximately 31% to 42%. This demonstrates that the present invention effectively improves the packaging bag's resistance to inner layer puncture caused by aluminum foil breakage.

[0115] The test results of Comparative Examples 2 and 3 were 12.1N and 12.8N, respectively. Although these were better than the traditional structure, they were significantly lower than those of Example 1 with the complete formulation. This performance difference indicates that there is a clear synergistic effect between PCL, EVA and nano silica. The absence of a single component will lead to a significant decrease in performance. This proves that the technical solution of the present invention achieves a technical effect that is better than the simple superposition of a single component through the synergy of multiple components.

[0116] Regarding biodegradability, all embodiments of this invention exhibited excellent biodegradability rates, exceeding 90% during the testing period, meeting the requirements for green packaging materials. In contrast, the conventional CPP material used in Comparative Example 1 showed no detectable biodegradability during testing, highlighting the substantial progress this invention makes in terms of environmental performance.

[0117] It is noteworthy that, due to the imbalance in the PBS matrix ratio, Comparative Example 4 exhibited a decrease in puncture resistance to 11.0 N, while its biodegradability also dropped to 89.5%. This phenomenon indicates that the specific ratio of each component is crucial for achieving a balance between mechanical and environmental performance. Although Example 4 possessed the highest puncture resistance, its biodegradability was slightly lower than that of the other examples, reflecting a common trade-off in material performance design.

[0118] In barrier performance testing, the embodiments of the present invention also demonstrated significant advantages. The oxygen and water vapor transmission rates of all embodiments remained at low levels, with the oxygen transmission rate of Embodiment 1 being 0.42 cm⁻¹. 3 / (m 2 ·d·atm), water vapor transmission rate is 0.68 g / (m 2 (d). This result is much lower than the corresponding value of the conventional CPP structure in Comparative Example 1, indicating that the packaging of the present invention has superior shelf-life performance.

[0119] Comparative Example 3, due to the lack of nano-silica, exhibited a significant decrease in barrier properties, with oxygen permeability increasing to 1.52 cm⁻¹. 3 / (m 2 The water vapor transmission rate increased to 2.40 g / (m·d·atm). 2 (d) This data change directly demonstrates the crucial role of nano-silica in enhancing the barrier properties of materials. Its effect of extending the permeation path of gas molecules, together with the aluminum foil layer, constructs a more complete dual barrier system.

[0120] Although the barrier performance of Comparative Example 2 was better than that of Comparative Example 3, it was still significantly lower than that of Example 1 with the complete formulation. This indicates that the addition of EVA indirectly promoted the uniform dispersion of nanoparticles by improving the internal phase structure of the material, thereby producing a synergistic enhancement effect on the barrier performance.

[0121] In summary, this invention, through the synergistic combination of specific components, significantly improves puncture resistance while also effectively enhancing the barrier properties of the packaging, providing more comprehensive protection for the contents. Example 4, with its highest nano-silica content, exhibits the best performance in both puncture resistance and barrier properties, while Example 1 achieves the optimal balance among these properties.

[0122] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. An aluminum foil bag for food packaging, comprising an outer layer, an aluminum foil layer, and an inner layer stacked sequentially from the outside to the inside, characterized in that, The inner layer is a puncture-resistant heat-sealing layer made of a composite material containing the following components in parts by weight: 65-85 parts polybutylene succinate; 10-25 parts polycaprolactone; 5-12 parts ethylene-vinyl acetate copolymer; and 1-5 parts nano-silica.

2. The aluminum foil bag for food packaging according to claim 1, characterized in that, The inner composite material also contains 0.3-1.0 parts of antioxidant 1010 and 0.5-2.0 parts of calcium stearate.

3. The aluminum foil bag for food packaging according to claim 1, characterized in that, The nano-silica is nano-silica with a surface modified by a silane coupling agent, and its particle size ranges from 20 to 60 nm.

4. The aluminum foil bag for food packaging according to claim 1, characterized in that, The inner layer has a puncture resistance of not less than 15N and a heat sealing strength of not less than 25N / 15mm.

5. The aluminum foil bag for food packaging according to claim 1, characterized in that, The outer layer is a polyethylene terephthalate film or a biaxially oriented polyamide film with a thickness of 12-25 μm; the aluminum foil layer has a thickness of 7-9 μm; and the inner layer has a thickness of 50-80 μm.

6. A manufacturing process for aluminum foil bags for food packaging according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix the components according to the formula using a high-speed mixer to obtain a premix; S2. The premixed material is fed into a twin-screw extruder, and after melt blending and extrusion granulation, inner layer composite material particles are obtained; wherein, the extruder processing temperature is 150-180℃; S3. The inner layer composite material particles are cast into a film using a casting extruder to form an inner layer film; S4. The outer film, aluminum foil layer and inner film are laminated using a dry laminator, water-based polyurethane adhesive is used, and the composite film is obtained after drying and curing. S5. The composite film is cut and heat-sealed into aluminum foil bags using a bag-making machine.

7. The preparation process according to claim 6, characterized in that, The twin-screw extruder described in step S2 has a length-to-diameter ratio of 40:1 to 48:1 and a screw speed of 200-300 rpm.

8. The preparation process according to claim 6, characterized in that, In step S3, during the casting process, the temperature of the cooling roller is controlled at 25-35℃.

9. The preparation process according to claim 6, characterized in that, The curing process described in step S4 is carried out at 45-55°C for 36-60 hours.

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