Sealing film suitable for ultra-high temperature environment and preparation process thereof

Abstract

The invention provides a sealing film suitable for an ultra-high-temperature environment and a preparation process thereof, and relates to the field of packaging. The packaging film comprises a PET layer, an aluminum foil layer and a heat-sealing layer, wherein the aluminum foil layer and the heat-sealing layer are connected through an adhesive; the heat-sealing layer is prepared from the following raw materials in parts by weight: 30 to 40 parts of linear low-density polyethylene, 20 to 30 parts of low-temperature heat-sealing resin, 25 to 30 parts of polyethylene glycol and 10 to 20 parts of ethylene-vinyl acetate copolymer; the sealing film is good in high-temperature resistance, stable in structure, high in strength and not prone to deformation in a high-temperature sterilization environment.

Description

Technical Field

[0001] This invention relates to the field of packaging, and more specifically, to a sealing film suitable for ultra-high temperature environments and its preparation process. Background Technology

[0002] Sealing film is a composite film material mainly used to seal containers to prevent substances inside from spilling out, evaporating, or releasing odors, thus avoiding bacterial contamination and extending shelf life. In the food industry, some food processing techniques require high-temperature sterilization after packaging, or consumers may need to cook the packaged food along with its container to preserve the original flavor of the ingredients.

[0003] Whether it's the initial high-temperature sterilization or the subsequent high-temperature cooking, the sealing film needs to withstand temperatures above 100℃. Currently, the main structure of water-resistant sealing films in existing technology consists of a PET layer, a printed layer, an aluminum foil layer, and a heat-sealing layer, with the layers connected by adhesives. During high-temperature cooking, the adhesives will fail, causing the layers to separate, resulting in wrinkles, delamination, or even breakage of the sealing film, leading to substandard product packaging. Summary of the Invention

[0004] The purpose of this invention is to provide a sealing film suitable for ultra-high temperature environments. It has good high temperature resistance, and the sealing film structure is stable, strong, and not easily deformed under high temperature sterilization conditions.

[0005] Another objective of this invention is to provide a process for preparing a sealing film suitable for ultra-high temperature environments, wherein the sealing film prepared by this process has good high temperature resistance.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] On one hand, embodiments of the present invention provide a sealing film suitable for ultra-high temperature environments, which includes a PET layer, an aluminum foil layer and a heat-sealing layer arranged sequentially, wherein the aluminum foil layer and the heat-sealing layer are connected by an adhesive; The heat-sealing layer comprises, by weight, the following raw materials: 30-40 parts of linear low-density polyethylene, 20-30 parts of low-temperature heat-sealing resin, 25-30 parts of polyethylene glycol, and 10-20 parts of ethylene-vinyl acetate copolymer. The adhesive comprises the following raw materials by weight: 10-20 parts polyurethane, 10-20 parts isocyanate, 5-10 parts ethyl acetate, 1-5 parts silane coupling agent, 1-3 parts tetrabutyl titanate, 1-5 parts polyurethane-isocyanate bilayer microcapsules, and 5-10 parts hydrogenated rosin glycerol ester. The polyurethane-isocyanate bilayer microcapsule is a bilayer core-shell structure with polyurethane and isocyanate as the core material and melamine resin as the wall material.

[0008] In some embodiments of the present invention, the polyurethane-isocyanate bilayer microcapsules are prepared by the following method: The liquid polyurethane prepolymer, emulsifier, and solvent are mixed evenly to obtain the first oil phase; The isocyanate prepolymer was mixed evenly with the emulsifier to obtain the second oil phase; The melamine resin prepolymer was mixed evenly with deionized water, and ammonium chloride solution was added to adjust the pH value to 4-5 to obtain the aqueous phase. Add the first oil phase dropwise to the aqueous phase and emulsify by high-speed shearing for 5-10 min. Then heat to 60-80℃ and stir for 1-3 h. Cool to room temperature, add coupling agent and stir evenly. Then add the second oil phase dropwise and emulsify by high-speed shearing for 5-10 min. Then heat to 60-80℃ and stir for 1-3 h. Centrifugation, vacuum drying, and pulverization were performed to obtain the polyurethane-isocyanate bilayer microcapsules. In some embodiments of the present invention, the molar ratio of the liquid polyurethane prepolymer to the isocyanate prepolymer is 1:(1-1.5). In some embodiments of the present invention, the molar ratio of the liquid polyurethane prepolymer to the melamine resin prepolymer is 1:(2-3). In some embodiments of the present invention, an ink printing layer is further included, the ink printing layer being printed on the aluminum foil layer, and the PET layer covering the ink printing layer.

[0009] In some embodiments of the present invention, the thickness of the PET layer is 10-20 μm, the thickness of the aluminum foil layer is 30-50 μm, and the thickness of the heat-sealing layer is 100-150 μm.

[0010] In some embodiments of the present invention, the low-temperature heat-sealing resin is one of ethylene-vinyl acetate copolymer, sarin resin, ethylene-methyl acrylate, and metallocene polyethylene-polypropylene copolymer.

[0011] On the other hand, embodiments of the present invention provide a process for preparing a sealing film suitable for ultra-high temperature environments, comprising the following steps: The raw materials for the heat-sealing layer are added to a blown film machine and blown film is formed to obtain a heat-sealing layer film; An adhesive is coated on both surfaces of an aluminum foil, and then a heat-sealing film and a PET film are respectively covered on them. The film is then hot-pressed to obtain a raw sealing film. The raw sealing film is placed in a curing chamber for curing to obtain the sealing film.

[0012] In some embodiments of the present invention, the adhesive coating amount is 5-8 g / m². 2 .

[0013] In some embodiments of the present invention, the temperature of hot-pressing composite is 50-80°C.

[0014] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: The sealing film provided by this invention has a multi-layer structure, consisting of a PET layer, an aluminum foil layer, and a heat-sealing layer, connected by an adhesive. The adhesive contains polyurethane-isocyanate bilayer microcapsules, forming a core-shell structure with polyurethane and isocyanate as the core material and melamine resin as the wall material. The melamine resin coating protects the polyurethane and isocyanate. During high-temperature sterilization or boiling, the high temperature causes the melamine resin shell to rupture, releasing the internal polyurethane and isocyanate core materials, which supplement the adhesive and improve its tack strength. Furthermore, the isocyanate undergoes a self-polymerization reaction, forming a three-dimensional network structure with the functional groups in the polyurethane and adhesive, increasing the adhesive's strength and preventing adhesive failure that could lead to delamination, bulging, or other defects in the sealing film. Additionally, the addition of hydrogenated rosin glycerol ester further enhances the adhesive's tackiness.

[0015] The sealing film provided by the present invention has a heat-sealing layer composed of linear low-density polyethylene, low-temperature heat-sealing resin, polyethylene glycol, and ethylene-vinyl acetate copolymer. The low-temperature heat-sealing resin can reduce the heat-sealing temperature of the heat-sealing layer to achieve low-temperature heat sealing. The addition of ethylene-vinyl acetate copolymer can reduce the heat-sealing temperature on the one hand, and improve the toughness of the heat-sealing layer on the other hand, making it less prone to cracking in high-temperature environments.

[0016] The sealing film preparation process provided by this invention combines a PET layer, an aluminum foil layer, and a heat-sealing layer together through hot-pressing and curing. During the hot-pressing process, the adhesive cures, firmly connecting the heat-sealing layer and the aluminum foil layer together. Based on the material of the heat-sealing layer and the composition of the adhesive, the sealing film has excellent high-temperature resistance, high strength, and can be heat-sealed at low temperatures. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a cross-sectional schematic diagram of the sealing film according to an embodiment of the present invention.

[0019] Icons: 1-PET layer, 2-aluminum foil layer, 3-heat seal layer. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0022] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0023] Example Prepare the raw materials for heat-sealing layer AF according to the proportions in Table 1.

[0024] Table 1. Raw material ratio (parts by weight) for heat-sealing layer AF.

[0025] In heat-sealing layers A and B, the low-temperature heat-sealing resin is a metallocene polyethylene-polypropylene copolymer; in heat-sealing layers C and D, the low-temperature heat-sealing resin is saline resin; and in heat-sealing layers E and F, the low-temperature heat-sealing resin is ethylene-methyl acrylate. The molecular weight of polyethylene glycol is 400 Da.

[0026] Prepare the raw materials for adhesives I-VI according to the proportions in Table 2.

[0027] Table 2 Raw material ratios (parts by weight) for adhesives I-VI

[0028] In adhesives I-III, the isocyanate is hexamethylene diisocyanate, and in adhesives IV-VI, the isocyanate is trimethylhexamethylene diisocyanate. The coupling agent is γ-aminopropyltriethoxysilane.

[0029] The bilayer microcapsule structure was prepared by the following method: The liquid polyurethane prepolymer, emulsifier (Span80), and solvent (ethanol) are mixed evenly to obtain the first oil phase; The isocyanate (hexamethylene diisocyanate) prepolymer was mixed evenly with the emulsifier (Span 80) to obtain the second oil phase; The melamine resin prepolymer was mixed evenly with deionized water, and ammonium chloride solution was added to adjust the pH value to 4-5 to obtain the aqueous phase. The first oil phase was added dropwise to the aqueous phase and sheared and emulsified at high speed (10000 rpm) for 10 min. Then the temperature was raised to 75±2℃ and stirred for 2 h. The temperature was lowered to room temperature, the coupling agent was added and stirred evenly, and then the second oil phase was added dropwise. The shearing and emulsification was carried out at high speed (10000 rpm) for 10 min. Then the temperature was raised to 75±2℃ and stirred for 2 h. Centrifugation, vacuum drying, and pulverization were performed to obtain the polyurethane-isocyanate bilayer microcapsules.

[0030] The molar ratio of liquid polyurethane prepolymer, isocyanate prepolymer, and melamine resin is 1:1.5:2. The amounts of emulsifier, solvent, and deionized water added are not specified; they can be added in equal or excess amounts. The melamine resin prepolymer is an initial polymer formed by the condensation reaction of melamine and formaldehyde. The liquid polyurethane prepolymer is an isocyanate-terminated (NCO) prepolymer, synthesized by reacting excess polyisocyanates (such as TDI and MDI) with polyether / polyester polyols. It has high activity of free NCO groups. The manufacturer is Jiangsu Qianmeite Polyurethane New Materials Co., Ltd.

[0031] The preparation method for each adhesive is as follows: simply mix all the raw materials evenly.

[0032] According to the sealing film parameters in Table 3, the sealing films of Examples 1-12 were prepared as follows.

[0033] Table 3 Sealing film parameters for Examples 1-12

[0034] The preparation process of sealing film is as follows: The raw materials for the heat-sealing layer are added to a blown film machine and blown film is formed to obtain a heat-sealing layer film; According to the coating amount in Table 3, apply adhesive to both surfaces of aluminum foil, dry the adhesive at 60°C, and then cover them with heat-sealing film and PET film respectively. The temperature of the hot press roller is 70°C, and hot pressing is performed to obtain the green sealing film. The raw sealing film is placed in a curing chamber, and the temperature of the curing chamber is controlled at 50°C for 90 hours to obtain the sealing film. (See attached image) Figure 1 As shown, from top to bottom, the layers are PET layer 1, aluminum foil layer 2, and heat-sealing layer 3.

[0035] Example 13 differs from Example 1 in that an ink printing layer is added. The specific preparation method of the sealing film is as follows: The raw materials for the heat-sealing layer are added to a blown film machine and blown film is formed to obtain a heat-sealing layer film; On one surface of the aluminum foil, ink is printed to form an ink printing layer. After the ink printing layer dries, an adhesive is coated on the other surface of the aluminum foil. The adhesive is dried at 60°C. Then, a heat-sealing film and a PET film are applied separately. The temperature of the hot press roller is 70°C, and the film is hot-pressed to obtain a raw sealing film. The raw sealing film is placed in a curing chamber, the temperature of which is controlled at 50°C, and cured for 90 hours to obtain the sealing film.

[0036] Example 14 differs from Example 1 in that the specific preparation method of its sealing film is as follows: The raw materials for the heat-sealing layer are added to a blown film machine and blown film is formed to obtain a heat-sealing layer film; According to the coating amount in Example 1, adhesive is coated on both surfaces of aluminum foil, the adhesive is dried at 60°C, and then heat-sealing film and PET film are respectively coated on. The temperature of the hot press roller is 80°C, and hot pressing is performed to obtain a green sealing film. The raw sealing film is placed in a curing chamber, the temperature of which is controlled at 60°C, and cured for 90 hours to obtain the sealing film.

[0037] Example 15 differs from Example 1 in that the specific preparation method of its sealing film is as follows: The raw materials for the heat-sealing layer are added to a blown film machine and blown film is formed to obtain a heat-sealing layer film; According to the coating amount in Example 1, adhesive is coated on both surfaces of aluminum foil, the adhesive is dried at 60°C, and then heat-sealing film and PET film are respectively coated on. The temperature of the hot press roller is 75°C, and hot pressing is performed to obtain a green sealing film. The raw sealing film is placed in a curing chamber, and the temperature of the curing chamber is controlled at 65°C for 90 hours to obtain the sealing film.

[0038] Comparative Example 1 The difference from Example 1 is that no double-layer microcapsules are added to the adhesive in this comparative example; the polyurethane is 12.5 parts, the isocyanate is 22.5 parts, and the remaining raw materials, preparation methods and sealing film parameters are the same as those in Example 1.

[0039] Comparative Example 2 The difference from Example 1 is that hydrogenated rosin glycerol ester is not added to the adhesive in this comparative example; the polyurethane is 12.5 parts, the isocyanate is 22.5 parts, and the remaining raw materials, preparation methods and sealing film parameters are the same as those in Example 1.

[0040] Experimental Example The sealing films prepared in the examples and comparative examples were used in a PP plastic box hot-press sealing production line for hot-press sealing, with 3000 films produced per group. They were then transferred to a high-temperature sterilization production line for sterilization. The number of bulges, delaminations, and tears in each group of sealing films was counted, and qualified products (100 films per group) were selected. After being placed at room temperature for 1 month, they were subjected to a steaming and heating treatment. The heating treatment conditions were: the products were placed in water, and after the water boiled, it was kept boiling for 5 minutes. The number of tears in the sealing films was then counted, and the results are shown in Table 4.

[0041] Table 4 Performance of various sealing films

[0042] As can be seen from Table 4 above, the sealing film of the embodiments exhibits a high pass rate after high-temperature sterilization and remains intact after secondary boiling, with a low probability of breakage. In Comparative Example 1, no double-layer microcapsules were added to the adhesive, which could not release polyurethane and isocyanate during high-temperature sterilization, thus failing to further improve the adhesive strength. Therefore, under high temperature, the heat-sealing layer and aluminum foil were more likely to delaminate, making the sealing film more prone to breakage and resulting in a high defect rate. Similarly, in Comparative Example 2, no hydrogenated rosin glycerol ester was added, and the adhesive's viscosity decreased accordingly at high temperatures. However, compared to Comparative Example 1, the defect rate of the sealing film was slightly lower, but still worse than that of the embodiments. This demonstrates that in this invention, the double-layer microcapsules and hydrogenated rosin glycerol ester work synergistically to improve the adhesive performance of the adhesive at high temperatures, thereby increasing the pass rate of the sealing film.

[0043] In summary, the sealing film provided in this embodiment of the invention has a multi-layer structure, consisting of a PET layer, an aluminum foil layer, and a heat-sealing layer. The layers are connected by an adhesive. The adhesive provided in this invention contains polyurethane-isocyanate bilayer microcapsules, which are a core-shell structure with polyurethane and isocyanate as the core material and melamine resin as the wall material. The melamine resin coating protects the polyurethane and isocyanate. During high-temperature sterilization or high-temperature boiling, the high-temperature environment causes the melamine resin shell to rupture, releasing the internal core material, polyurethane and isocyanate, which can supplement the adhesive and improve its adhesive strength. Furthermore, the isocyanate can undergo a self-polymerization reaction, forming a three-dimensional network structure with the functional groups in the polyurethane and adhesive, improving the strength of the adhesive and preventing adhesive failure, which could lead to delamination, bulging, or other defects in the sealing film.

[0044] The sealing film provided by the present invention has a heat-sealing layer composed of linear low-density polyethylene, low-temperature heat-sealing resin, polyethylene glycol, and ethylene-vinyl acetate copolymer. The low-temperature heat-sealing resin can reduce the heat-sealing temperature of the heat-sealing layer to achieve low-temperature heat sealing. The addition of ethylene-vinyl acetate copolymer can reduce the heat-sealing temperature on the one hand, and improve the toughness of the heat-sealing layer on the other hand, making it less prone to cracking in high-temperature environments.

[0045] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A sealing film suitable for ultra-high temperature environments, characterized in that, It includes a PET layer, an aluminum foil layer and a heat-sealing layer arranged in sequence, wherein the aluminum foil layer and the heat-sealing layer are connected by an adhesive; The heat-sealing layer comprises, by weight, the following raw materials: 30-40 parts of linear low-density polyethylene, 20-30 parts of low-temperature heat-sealing resin, 25-30 parts of polyethylene glycol, and 10-20 parts of ethylene-vinyl acetate copolymer. The adhesive comprises the following raw materials by weight: 10-20 parts polyurethane, 10-20 parts isocyanate, 5-10 parts ethyl acetate, 1-5 parts silane coupling agent, 1-3 parts tetrabutyl titanate, 1-5 parts polyurethane-isocyanate bilayer microcapsules, and 5-10 parts hydrogenated rosin glycerol ester. The polyurethane-isocyanate bilayer microcapsule is a bilayer core-shell structure with polyurethane and isocyanate as the core material and melamine resin as the wall material.

2. The sealing film suitable for ultra-high temperature environments according to claim 1, characterized in that, The polyurethane-isocyanate bilayer microcapsules were prepared by the following method: The liquid polyurethane prepolymer, emulsifier, and solvent are mixed evenly to obtain the first oil phase; The isocyanate prepolymer was mixed evenly with the emulsifier to obtain the second oil phase; The melamine resin prepolymer was mixed evenly with deionized water, and ammonium chloride solution was added to adjust the pH value to 4-5 to obtain the aqueous phase. Add the first oil phase dropwise to the aqueous phase and emulsify by high-speed shearing for 5-10 min. Then heat to 60-80℃ and stir for 1-3 h. Cool to room temperature, add coupling agent and stir evenly. Then add the second oil phase dropwise and emulsify by high-speed shearing for 5-10 min. Then heat to 60-80℃ and stir for 1-3 h. Centrifugation, vacuum drying, and pulverization were performed to obtain the polyurethane-isocyanate bilayer microcapsules.

3. The sealing film suitable for ultra-high temperature environments according to claim 2, characterized in that, The molar ratio of the liquid polyurethane prepolymer to the isocyanate prepolymer is 1:(1-1.5).

4. The sealing film suitable for ultra-high temperature environments according to claim 2, characterized in that, The molar ratio of the liquid polyurethane prepolymer to the melamine resin prepolymer is 1:(2-3).

5. The sealing film suitable for ultra-high temperature environments according to claim 1, characterized in that, It also includes an ink printing layer, which is printed on the aluminum foil layer, and the PET layer covers the ink printing layer.

6. The sealing film suitable for ultra-high temperature environments according to claim 1, characterized in that, The PET layer has a thickness of 10-20 μm, the aluminum foil layer has a thickness of 30-50 μm, and the heat-sealing layer has a thickness of 100-150 μm.

7. The sealing film suitable for ultra-high temperature environments according to claim 1, characterized in that, The low-temperature heat-sealing resin is one of ethylene-vinyl acetate copolymer, sarin resin, ethylene-methyl acrylate, and metallocene polyethylene-polypropylene copolymer.

8. A process for preparing a sealing film suitable for ultra-high temperature environments as described in any one of claims 1-7, characterized in that, Includes the following steps: The raw materials for the heat-sealing layer are added to a blown film machine and blown film is formed to obtain a heat-sealing layer film; An adhesive is coated on both surfaces of an aluminum foil, and then a heat-sealing film and a PET film are respectively covered on them. The film is then hot-pressed to obtain a raw sealing film. The raw sealing film is placed in a curing chamber for curing to obtain the sealing film.

9. The preparation process of the sealing film suitable for ultra-high temperature environments according to claim 8, characterized in that, The adhesive coating amount is 5-8 g / m². 2 .

10. The preparation process of the sealing film suitable for ultra-high temperature environments according to claim 8, characterized in that, The temperature for hot pressing is 50-80℃.

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