Aluminum foil easy-to-tear cover capable of being cooked at high temperature and preparation process thereof

Abstract

The invention provides a high-temperature cooking aluminum foil easy-to-tear cover and a preparation process thereof, and belongs to the technical field of easy-to-tear covers. According to the aluminum foil easy-to-tear cover capable of being used for high-temperature cooking, the protective layer, the first reinforcing layer, the aluminum foil layer, the second reinforcing layer and the heat sealing layer are connected in an adhesive mode, and compared with an existing aluminum foil easy-to-tear cover, phenolic acid and inorganic nano particle cross-linked modified polyvinyl alcohol with the antibacterial effect serve as the protective layer; the blocking capacity and stability of the aluminum foil easy-to-tear cover can be improved, corrosion and damage of the external environment to the aluminum foil easy-to-tear cover are effectively prevented, the storage stability of the aluminum foil easy-to-tear cover is improved, and the service life of the aluminum foil easy-to-tear cover is prolonged; meanwhile, the first reinforcing layer and the second reinforcing layer are arranged on the two sides of the aluminum foil layer respectively and are made of the composite reinforcing materials, under the action of all components of the composite reinforcing materials, the stability of the aluminum foil easy-to-tear cover is further improved, and the phenomena of damage, layering and the like at high temperature are prevented.

Description

Technical Field

[0001] The invention relates to the technical field of easy-tear covers, and in particular to an aluminum foil easy-tear cover capable of being steamed at high temperature and a preparation process thereof. Background Art

[0002] As a new type of packaging material, aluminum foil easy-tear cover is widely used in food, beverage, medicine, cosmetics and other fields because of its advantages such as non-toxic, odorless, beautiful, easy to open and recyclable.

[0003] Traditional aluminum foil easy-tear covers generally adopt a structure of varnish / aluminum foil / polyethylene (PE). When the contents are sealed and sterilized during high-temperature cooking or hot filling at 90°C, phenomena such as film stratification and cup leakage may occur. In order to strengthen the strength of the easy-tear cover film, nylon material is used as a reinforcing base to improve the heat resistance of the aluminum foil easy-tear cover. For example, Chinese patent CN201811215593.8 discloses an easy-tear cover with a retort-resistant aluminum foil, the easy-tear cover comprising a cover body provided with a food inlet and outlet and an easy-tear cover aluminum foil, the easy-tear cover aluminum foil comprising an aluminum foil body, a color layer, a protective layer, a composite adhesive layer one, a nylon film layer, a composite adhesive layer two and a PP film layer. Although the easy-tear cover has certain retort resistance and is reusable, under high-temperature retort conditions, the strength of the nylon film layer will decrease due to the influence of high temperature or absorption of moisture, resulting in leakage or film stratification, thereby reducing the use quality of the easy-tear cover. At the same time, the aluminum foil easy-tear cover is not provided with a reinforcing layer, and the overall strength and stability of the aluminum foil easy-tear cover cannot be effectively improved. It is prone to breakage and stratification under high temperature and pressure, thereby affecting the protection and sealing of the package contents, and also reducing the user experience and market trust.

[0004] Therefore, there is an urgent need to provide an aluminum foil easy-tear cover with good stability and can be used for high-temperature cooking. Summary of the invention

[0005] In view of the defects of the prior art, the present invention designs an aluminum foil easy-tear cover which is adhesively connected by a protective layer, a first reinforcement layer, an aluminum foil layer, a second reinforcement layer, and a heat-sealing layer. The cover can be used for high-temperature cooking, has good stability, and improves the quality of the product.

[0006] In order to achieve the above purpose, the present invention solves the technical problem by adopting the following technical solutions:

[0007] In a first aspect, the present invention provides an aluminum foil easy-tear cover that can be steamed at high temperature, the aluminum foil easy-tear cover comprising a protective layer (1), a first reinforcement layer (2), an aluminum foil layer (3), a second reinforcement layer (4), and a heat-sealing layer (5); wherein the protective layer (1) is adhesively connected to the first reinforcement layer (2), the first reinforcement layer (2) is adhesively connected to the aluminum foil layer (3), the aluminum foil layer (3) is adhesively connected to the second reinforcement layer (4), and the second reinforcement layer (4) is adhesively connected to the heat-sealing layer (5).

[0008] In some embodiments, the protective layer (1) is made of a modified polyvinyl alcohol material, and the preparation of the modified polyvinyl alcohol material comprises the following steps:

[0009] S1. After adding nano-titanium dioxide to anhydrous ethanol for ultrasonic pretreatment for 15-25 minutes, add it to a 13-17wt% PVA solution and stir at 75-85°C for 30-50 minutes to obtain a PVA suspension;

[0010] S2. Add the gentisic acid solution to the PVA suspension and react at 75-85°C for 2-4 hours. After the reaction is completed, cool and dry to obtain a modified polyvinyl alcohol material.

[0011] In some of the embodiments, the first reinforcement layer (2) and the second reinforcement layer (4) are both made of a composite reinforcement material, which comprises, by mass, 50-60 parts of polyethylene terephthalate, 8-12 parts of polypropylene fibers, 3-7 parts of basalt fibers, 3-7 parts of chitosan nanowhiskers, 4-7 parts of thermoplastic elastomers, 2-3 parts of stabilizers, 0.5-1 parts of coupling agents, and 0.3-0.5 parts of dispersants.

[0012] In some of the embodiments, the composite reinforcement material includes, by mass, 55 parts of polyethylene terephthalate, 10 parts of polypropylene fiber, 5 parts of basalt fiber, 5 parts of chitin nanowhiskers, 5 parts of thermoplastic elastomer, 2.5 parts of stabilizer, 0.8 parts of coupling agent, and 0.4 parts of dispersant.

[0013] In some embodiments, the stabilizer is one or more of dimethyl dimercaptoacetate isooctyltin, di-n-octyltin bis(isooctylthioacetate), methyl tin mercaptan, octyl tin mercaptan, butyl tin mercaptan, and dimethyl tin oxide.

[0014] In some embodiments, the coupling agent is a silane coupling agent.

[0015] In some embodiments, the dispersant is an amide lubricating dispersant.

[0016] In some of the embodiments, the heat sealing layer (5) is formed by coating a heat sealing liquid, and the heat sealing liquid comprises the following components in parts by mass: 30-40 parts of thermoplastic acrylic resin, 20-30 parts of phenolic resin, 8-12 parts of polyolefin elastomer, 3-8 parts of nano calcium carbonate, 6-10 parts of liquid paraffin, 2-4 parts of β-(4-hydroxy-3,5-di-tert-butylphenyl) propionate, and 0.5-1.5 parts of isocyanate curing agent.

[0017] In a second aspect, the present invention provides a method for preparing an aluminum foil easy-tear cover that can be steamed at high temperature, wherein a protective layer, a first reinforcement layer, an aluminum foil layer, a second reinforcement layer, and a heat-sealing layer are prepared separately, and then the protective layer, the first reinforcement layer, the aluminum foil layer, the second reinforcement layer, and the heat-sealing layer are connected together with an adhesive.

[0018] Among them, the protective layer is used to prevent the external environment from corroding and damaging the aluminum foil easy-tear cover; the aluminum foil layer is used to provide barrier properties and effectively block oxygen and water vapor; the reinforcement layer is used to improve the strength and high temperature resistance of the easy-tear cover; the heat sealing layer is used to achieve heat sealing between the easy-tear cover and the packaging container.

[0019] In some of the embodiments, it is characterized in that the adhesive is a solvent-based two-component polyurethane adhesive.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The invention provides an aluminum foil easy-tear cover which can be used for high-temperature cooking and is adhesively connected by a protective layer, a first reinforcement layer, an aluminum foil layer, a second reinforcement layer and a heat-sealing layer. Compared with the existing aluminum foil easy-tear cover, the invention uses gentisic acid with antibacterial effect and inorganic nanoparticle cross-linked modified polyvinyl alcohol as the protective layer, which can improve the barrier capacity of the protective layer, and the gentisic acid contains phenolic hydroxyl groups, which further improves the stability of the protective layer, thereby effectively preventing the external environment from corroding and damaging the aluminum foil easy-tear cover, improving the storage stability of the aluminum foil easy-tear cover, and extending its service life.

[0022] The present invention also arranges a first reinforcement layer and a second reinforcement layer on both sides of the aluminum foil layer, both of which are made of composite reinforcement materials. Under the action of various components of the composite reinforcement material, the stability of the aluminum foil easy-tear cover is effectively improved to prevent damage and delamination at high temperatures.

[0023] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the implementation mode will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a schematic diagram of the structure of the high temperature steamable aluminum foil easy-tear cover in an embodiment of the present invention.

[0026] Description of reference numerals:

[0027] 1. Protective layer; 2. First reinforcement layer; 3. Aluminum foil layer; 4. Second reinforcement layer; 5. Heat sealing layer. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0030] In the present invention, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0031] In the present invention, the test methods used are conventional methods unless otherwise specified; the materials, reagents, etc. used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0032] In the present invention, the particle size of the "nano titanium dioxide" used is 10-20 nm.

[0033] The embodiment of the present invention provides a high temperature steamable aluminum foil easy-tear cover, comprising a protective layer 1, a first reinforcement layer 2, an aluminum foil layer 3, a second reinforcement layer 4, and a heat sealing layer 5; Figure 1As shown, the protective layer 1 is adhesively connected to one side of the first reinforcement layer 2, the first reinforcement layer 2 is adhesively connected to one side of the aluminum foil layer 3 away from the protective layer 1, the aluminum foil layer 3 is adhesively connected to one side of the second reinforcement layer 4 away from the first reinforcement layer 2, and the second reinforcement layer 4 is adhesively connected to one side of the heat sealing layer 5 away from the aluminum foil layer 3.

[0034] Specifically, the thickness of the protective layer 1 is 0.08-0.1 mm; the thickness of the first reinforcement layer 2 and the second reinforcement layer 4 are both 0.08-0.1 mm; the thickness of the aluminum foil layer 3 is 0.15-0.2 mm; and the thickness of the heat sealing layer is 0.05-0.1 mm.

[0035] Example 1

[0036] 1. A high-temperature steamable aluminum foil easy-tear cover, comprising a protective layer, a first reinforcement layer, an aluminum foil layer, a second reinforcement layer, and a heat-sealing layer;

[0037] In this embodiment, the protective layer is made of a modified polyvinyl alcohol film, and the preparation of the modified polyvinyl alcohol film includes the following steps:

[0038] (1) Weigh 50 g of PVA particles and add them into distilled water, place them in a constant temperature of 90° C. and stir them to dissolve (stirring speed is 300 rpm) to obtain a transparent PVA solution with a mass fraction of 15%;

[0039] (2) Add nano-titanium dioxide (2% of the amount of PVA particles) to anhydrous ethanol at a solid-liquid ratio of 1:80 (g / mL), stir for 10 min, and then ultrasonically treat for 20 min (frequency is 30 kHz). Slowly pour the obtained nano-titanium dioxide solution into the PVA solution, stir at 80°C for 40 min (stirring speed is 800 rpm) to obtain a PVA suspension;

[0040] (3) Gentisic acid (6% of the amount of PVA particles) was dissolved in an appropriate amount of distilled water, and then added to the PVA suspension to react at 80° C. for 2 h. After the reaction, the reaction solution was cooled to room temperature, poured into a glass dish, vacuum dried at 60° C. for 12 h, and cooled to room temperature to obtain a modified polyvinyl alcohol film 1.

[0041] In this embodiment, the first reinforcement layer and the second reinforcement layer are both made of a composite reinforcement material, which includes, by mass, 50 parts of polyethylene terephthalate, 12 parts of polypropylene fiber, 3 parts of basalt fiber, 7 parts of chitin nanowhiskers, 4 parts of thermoplastic elastomer (styrene-butadiene block copolymer), 3 parts of stabilizer (di-n-octyltin dithioacetate), 1 part of coupling agent (KH-550), and 0.3 dispersant (TAS-2A).

[0042] Polyethylene terephthalate, polypropylene fiber, basalt fiber, chitosan nano whisker, thermoplastic elastomer, stabilizer, dispersant and coupling agent are premixed and added into a twin-screw extruder for melt mixing and extrusion granulation. The extrusion temperature is 230°C and the screw speed is 400r / min.

[0043] In this embodiment, the heat sealing layer is formed by coating a heat sealing liquid, and the heat sealing liquid includes the following components by mass: 35 parts of thermoplastic acrylic resin, 25 parts of phenolic resin, 10 parts of polyolefin elastomer (POE), 5 parts of nano calcium carbonate, 8 parts of liquid paraffin, 3 parts of β-(4-hydroxy-3,5-di-tert-butylphenyl) propionate, and 1 part of isocyanate curing agent (HI-100).

[0044] 2. A method for preparing an aluminum foil easy-tear cover that can be steamed at high temperature, comprising the following steps:

[0045] The protective layer, the first reinforcement layer, the aluminum foil layer, the second reinforcement layer and the heat-sealing layer are connected by a solvent-based two-component polyurethane adhesive to obtain an aluminum foil easy-tear cover that can be steamed at high temperature.

[0046] Example 2

[0047] 1. A high-temperature steamable aluminum foil easy-tear cover, comprising a protective layer, a first reinforcement layer, an aluminum foil layer, a second reinforcement layer, and a heat-sealing layer;

[0048] In this embodiment, the protective layer is made of a modified polyvinyl alcohol film, and the preparation of the modified polyvinyl alcohol film includes the following steps:

[0049] The preparation of the modified polyvinyl alcohol film comprises the following steps:

[0050] (1) Weigh 50 g of PVA particles and add them into distilled water, place them in a constant temperature of 90° C. and stir them to dissolve (stirring speed is 300 rpm) to obtain a transparent PVA solution with a mass fraction of 13%;

[0051] (2) Add nano-titanium dioxide (3% of the amount of PVA particles) to anhydrous ethanol at a solid-liquid ratio of 1:80 (g / mL), stir for 10 min, and then ultrasonically treat for 25 min (frequency is 30 kHz). Slowly pour the obtained nano-titanium dioxide solution into the PVA solution, stir at 85°C for 50 min (stirring speed is 600 rpm) to obtain a PVA suspension;

[0052] (3) Gentisic acid (4% of the amount of PVA particles) was dissolved in an appropriate amount of distilled water, and then added to the PVA suspension to react at 85°C for 4 hours. After the reaction, the reaction solution was cooled to room temperature, poured into a glass dish, vacuum dried at 60°C for 12 hours, and cooled to room temperature to obtain a modified polyvinyl alcohol film 2.

[0053] In this embodiment, the first reinforcement layer and the second reinforcement layer are both made of a composite reinforcement material, which includes, by mass, 55 parts of polyethylene terephthalate, 10 parts of polypropylene fiber, 5 parts of basalt fiber, 5 parts of chitin nanowhiskers, 5 parts of thermoplastic elastomer (styrene-butadiene block copolymer), 2.5 parts of stabilizer (methyl tin mercaptan), 0.8 parts of coupling agent (KH-540), and 0.4 dispersant (TAS-2A).

[0054] Polyethylene terephthalate, polypropylene fiber, basalt fiber, chitosan nano whisker, thermoplastic elastomer, stabilizer, dispersant and coupling agent are premixed and added into a twin-screw extruder for melt mixing and extrusion granulation. The extrusion temperature is 220°C and the screw speed is 300r / min.

[0055] In this embodiment, the heat sealing layer is formed by coating a heat sealing liquid, and the heat sealing liquid includes the following components by mass: 30 parts of thermoplastic acrylic resin, 30 parts of phenolic resin, 12 parts of polyolefin elastomer (POE), 3 parts of nano calcium carbonate, 6 parts of liquid paraffin, 2 parts of β-(4-hydroxy-3,5-di-tert-butylphenyl) propionate, and 1.5 parts of isocyanate curing agent (HI-100).

[0056] 2. A method for preparing a high temperature steamable aluminum foil easy-tear cover is the same as that in Example 1.

[0057] Example 3

[0058] 1. A high-temperature steamable aluminum foil easy-tear cover, comprising a protective layer, a first reinforcement layer, an aluminum foil layer, a second reinforcement layer, and a heat-sealing layer;

[0059] In this embodiment, the protective layer is made of a modified polyvinyl alcohol film, and the preparation of the modified polyvinyl alcohol film includes the following steps:

[0060] The preparation of the modified polyvinyl alcohol film comprises the following steps:

[0061] (1) Weigh 50 g of PVA particles and add them into distilled water, place them in a constant temperature of 90° C. and stir them to dissolve (stirring speed is 300 rpm) to obtain a transparent PVA solution with a mass fraction of 17%;

[0062] (2) Nano-titanium dioxide (1% of the amount of PVA particles) was added to anhydrous ethanol at a solid-liquid ratio of 1:80 (g / mL), stirred for 10 min, and then ultrasonically treated for 15 min (frequency of 30 kHz). The obtained nano-titanium dioxide solution was slowly poured into the PVA solution and stirred at 75°C for 30 min (stirring speed of 1000 rpm) to obtain a PVA suspension;

[0063] (3) Gentisic acid (8% of the amount of PVA particles) was dissolved in an appropriate amount of distilled water, and then added to the PVA suspension to react at 75°C for 2 hours. After the reaction, the reaction solution was cooled to room temperature, poured into a glass dish, vacuum dried at 60°C for 12 hours, and cooled to room temperature to obtain a modified polyvinyl alcohol film 3.

[0064] In this embodiment, the first reinforcement layer and the second reinforcement layer are both made of a composite reinforcement material, which includes, by mass, 60 parts of polyethylene terephthalate, 8 parts of polypropylene fiber, 7 parts of basalt fiber, 3 parts of chitin nanowhiskers, 7 parts of thermoplastic elastomer (ethylene-octene copolymer), 2 parts of stabilizer (octyl tin mercaptan), 0.5 parts of coupling agent (KH-590), and 0.5 parts of dispersant (TAS-2A).

[0065] Polyethylene terephthalate, polypropylene fiber, basalt fiber, chitosan nano whisker, thermoplastic elastomer, stabilizer, dispersant and coupling agent are premixed and added into a twin-screw extruder for melt mixing and extrusion granulation. The extrusion temperature is 210°C and the screw speed is 200r / min.

[0066] In this embodiment, the heat sealing layer is formed by coating a heat sealing liquid, and the heat sealing liquid includes the following components by mass: 40 parts of thermoplastic acrylic resin, 20 parts of phenolic resin, 8 parts of polyolefin elastomer (POE), 3 parts of nano calcium carbonate, 10 parts of liquid paraffin, 4 parts of β-(4-hydroxy-3,5-di-tert-butylphenyl) propionate, and 0.5 parts of isocyanate curing agent (HI-100).

[0067] 2. A method for preparing a high temperature steamable aluminum foil easy-tear cover is the same as that in Example 1.

[0068] Comparative Example 1

[0069] The difference between Comparative Example 1 and Example 1 is that the modified polyvinyl alcohol film is replaced by pure PVA film in Comparative Example 1, and the other contents are the same.

[0070] Comparative Example 2

[0071] The difference between Comparative Example 2 and Example 1 is that, in the preparation of the modified polyvinyl alcohol film, gallic acid is used instead of chlorogenic acid in Comparative Example 2, and the other contents are the same.

[0072] Comparative Example 3

[0073] The difference between Comparative Example 3 and Example 1 is that the first reinforcement layer and the second reinforcement layer are not added in Comparative Example 3, and the other parts are the same.

[0074] Comparative Example 4

[0075] The difference between Comparative Example 4 and Example 1 is that the reinforced composite material is different, and the other aspects are the same.

[0076] The reinforced composite material comprises, by mass, 55 parts of polyethylene terephthalate, 10 parts of polypropylene fiber, 5 parts of basalt fiber, 5 parts of thermoplastic elastomer (styrene-butadiene block copolymer), 2.5 parts of stabilizer (dioctyltin dilaurate), 0.8 parts of coupling agent (KH-540), and 0.4 parts of dispersant (TAS-2A).

[0077] Test Example 1

[0078] 1. Barrier properties

[0079] 1. According to GB / T 1037-2021 "Determination of water vapor permeability of plastic film and sheeting - Cup weight gain and weight loss method", the water vapor permeability of the aluminum foil easy-tear cover is tested. The test conditions are: 23℃±0.5℃, relative humidity is 90%±2%; the test time is 24h. The test is repeated three times and the results are averaged.

[0080] 2. According to GB / T 1038.1-2022 "Plastic film and sheet gas permeability test method Part 1: Differential pressure method", test the oxygen barrier property of the aluminum foil easy-tear cover. Test conditions: 23℃±2℃. Test time: 48h. Repeat the test three times and take the average value of the results.

[0081] 2. Cooking resistance: Cooking at 121℃ for 30min, the cover film has no delamination and the cover ring does not fall off.

[0082] 3. Chemical stability: toluene diamine (4% acetic acid, 121°C, 2h).

[0083] Table 1 Aluminum foil easy-tear cover performance test results

[0084]

[0085]

[0086] It can be seen from Table 1 that the water vapor permeability of the aluminum foil easy-tear covers of Examples 1-3 is less than 0.5 g / (m 2 ·24h), oxygen permeability: ≤0.5cm 3 / (m 2 ·24h·0.1MPa), indicating that the aluminum foil easy-tear cover of the present invention has good barrier properties; then comparing comparative examples 1 and 2 with embodiment 1, the water vapor permeability and oxygen permeability of embodiment 1 are significantly reduced. This is because the phenolic acid grafted modified polyvinyl alcohol not only further fills the pores of polyvinyl alcohol, but also has antioxidant properties, thereby increasing the barrier properties and stability of the aluminum foil easy-tear cover. Moreover, compared with gallic acid, the gentisic acid with poor water solubility used in the embodiment has better water vapor barrier properties.

[0087] At the same time, in comparison examples 3 and 4 and Example 1, the present invention cooperates with each other and works synergistically among polyethylene terephthalate, polypropylene fiber, basalt fiber, chitosan nano whisker, thermoplastic elastomer, stabilizer, coupling agent and dispersant to prepare the first reinforcement layer and the second reinforcement layer, which can improve the stability of the aluminum foil easy-tear cover and extend its service life.

[0088] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A high temperature steamable aluminum foil easy-tear cover, characterized in that: The aluminum foil easy-tear cover comprises a protective layer (1), a first reinforcement layer (2), an aluminum foil layer (3), a second reinforcement layer (4), and a heat-sealing layer (5); wherein the protective layer (1) is adhesively connected to the first reinforcement layer (2), the first reinforcement layer (2) is adhesively connected to the aluminum foil layer (3), the aluminum foil layer (3) is adhesively connected to the second reinforcement layer (4), and the second reinforcement layer (4) is adhesively connected to the heat-sealing layer (5).

2. The high temperature steamable aluminum foil easy-tear cover according to claim 1, characterized in that: The protective layer (1) is made of modified polyvinyl alcohol material, and the preparation of the modified polyvinyl alcohol material comprises the following steps: S1. After adding nano-titanium dioxide to anhydrous ethanol for ultrasonic pretreatment for 15-25 minutes, add it to a 13-17wt% PVA solution and stir at 75-85°C for 30-50 minutes to obtain a PVA suspension; S2. Add the gentisic acid solution to the PVA suspension and react at 75-85°C for 2-4 hours. After the reaction is completed, cool and dry to obtain a modified polyvinyl alcohol material.

3. The high temperature steamable aluminum foil easy-tear cover according to claim 1, characterized in that: The first reinforcement layer (2) and the second reinforcement layer (4) are both made of a composite reinforcement material, which comprises, by weight, 50-60 parts of polyethylene terephthalate, 8-12 parts of polypropylene fibers, 3-7 parts of basalt fibers, 3-7 parts of chitin nano whiskers, 4-7 parts of thermoplastic elastomers, 2-3 parts of stabilizers, 0.5-1 parts of coupling agents, and 0.3-0.5 parts of dispersants.

4. The high temperature steamable aluminum foil easy-tear cover according to claim 3, characterized in that: The composite reinforcement material comprises, by mass, 55 parts of polyethylene terephthalate, 10 parts of polypropylene fiber, 5 parts of basalt fiber, 5 parts of chitin nano whiskers, 5 parts of thermoplastic elastomer, 2.5 parts of stabilizer, 0.8 parts of coupling agent, and 0.4 parts of dispersant.

5. The high temperature steamable aluminum foil easy-tear cover according to claim 3, characterized in that: The stabilizer is one or more of dimethyl dimercaptoacetate isooctyl tin, di-n-octyl tin bis(isooctyl thioglycolate), methyl tin mercaptan, octyl tin mercaptan, butyl tin mercaptan, and dimethyl tin oxide.

6. The high temperature steamable aluminum foil easy-tear cover according to claim 3, characterized in that: The coupling agent is a silane coupling agent.

7. The high temperature steamable aluminum foil easy-tear cover according to claim 3, characterized in that: The dispersant is an amide lubricating dispersant.

8. The high temperature steamable aluminum foil easy-tear cover according to claim 1, characterized in that: The heat-sealing layer (5) is formed by coating a heat-sealing liquid, wherein the heat-sealing liquid comprises the following components in parts by mass: 30-40 parts of a thermoplastic acrylic resin, 20-30 parts of a phenolic resin, 8-12 parts of a polyolefin elastomer, 3-8 parts of nano-calcium carbonate, 6-10 parts of liquid paraffin, 2-4 parts of n-octadecyl β-(4-hydroxy-3,5-di-tert-butylphenyl) propionate, and 0.5-1.5 parts of an isocyanate curing agent.

9. A method for preparing an aluminum foil easy-tear cover that can be steamed at high temperature, characterized in that: First, prepare the protective layer, the first reinforcement layer, the aluminum foil layer, the second reinforcement layer, and the heat-sealing layer respectively, and then connect the protective layer, the first reinforcement layer, the aluminum foil layer, the second reinforcement layer, and the heat-sealing layer with an adhesive.

10. The method for preparing the high temperature steamable aluminum foil easy-tear cover according to claim 9, characterized in that: The adhesive is a solvent-based two-component polyurethane adhesive.

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