Cooking-resistant easy-to-tear composite film and preparation method thereof

Abstract

The invention relates to a cooking-resistant easy-to-tear composite film and a preparation method thereof. The cooking-resistant easy-to-tear composite film is formed by integrally connecting a polyolefin heat-sealing layer, an easy-to-tear layer, a core layer and a composite layer through co-extrusion film blowing or curtain coating. And the polyolefin heat sealing layer is made of a polypropylene mixture and is added with 2-6% of opening smooth master batch. The easy-to-tear layer consists of a hydrogenated polystyrene elastomer, polybutylene and maleic anhydride grafted polypropylene. And the core layer is made of polypropylene or olefin copolymer. And the composite layer is made of corona-treated polyolefin. According to the preparation method, the composite film is prepared through multi-layer co-extrusion casting, can tolerate high-temperature cooking at 135-141 DEG C for 40 minutes, is stable in heat sealing strength, is free of wiredrawing phenomenon when being uncovered, is uniform in blank leaving, is suitable for packaging of metal cans, standing pouches and the like, and meets the high-sterilization requirements of cooked food, milk powder and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soft packaging, in particular to a composite film capable of resisting 135-141℃ cooking and having stable easy-to-peel performance and a preparation method thereof. BACKGROUND

[0002] Many foods such as cans, vacuum-packed meat, and sauces need to be sterilized by high-temperature cooking to kill microorganisms and prolong shelf life. Ordinary plastic film cannot withstand high temperatures, while high-temperature-resistant composite film can ensure that the package does not break or deform during sterilization. However, the easy-to-peel force of the current high-temperature cooking easy-to-peel composite film varies with the heat sealing temperature and cannot be stabilized within a certain range. The easy-to-peel force value of the composite film after heat sealing or self-sealing is difficult to control, and different easy-to-peel force values of the same product bring consumers an unpleasant experience.

[0003] In addition, the traditional cooking-resistant composite film produces serious stringing when peeled, leaving uneven white space, and after heat sealing with other substrates, it cannot bring consumers a good visual effect, reducing the attractiveness of the product. In addition, the current cooking-resistant composite film such as CN113427871A and CN101987674A can only achieve a technical effect of cooking at 121-130℃ for 30min, which cannot meet the packaging needs of foods with high sterilization requirements, and easy-to-peel composite films after cooking often have wrinkles, delamination, or bag breakage.

[0004] The utility model patent with the publication number CN221819666U provides an easy-to-tear and easy-to-peel film as the prior application of the patentee, but the technical solution lacks related design for high-temperature cooking. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a cooking-resistant easy-to-peel composite film that can resist 135-141℃ cooking and has a good appearance after cooking without wrinkles or bubbles. The easy-to-peel composite film also has stable easy-to-peel force, and the same easy-to-peel force value can be achieved at a heat sealing temperature of 130-180℃.

[0006] To achieve the above-mentioned purpose, the present application provides a cooking-resistant easy-to-peel composite film, which comprises a polyolefin heat sealing layer, an easy-to-peel layer, a core layer, and a composite layer connected integrally by blending and blowing film or casting coating in sequence. The polyolefin heat sealing layer is made of at least one of polypropylene, modified polypropylene, and ethylene-propylene copolymer and contains 2-6% of opening and smoothness masterbatch based on the mass of the polyolefin heat sealing layer. The easy-to-peel layer is made of hydrogenated polystyrene elastomer and / or polybutene and contains 2-10% of maleic anhydride grafted polypropylene based on the total mass of the easy-to-peel layer. The easy-to-peel force value is adjusted by adjusting the ratio of hydrogenated polystyrene elastomer and polybutene. The core layer is made of at least one of polypropylene, ethylene-propylene copolymer, ethylene-hexene copolymer and ethylene-heptene copolymer. The composite layer is made of polyolefin subjected to surface corona treatment.

[0007] As an explanatory description, the polypropylene in the polyolefin heat-seal layer is preferably homopolymer polypropylene, the modified polypropylene is preferably maleic anhydride grafted polypropylene with a grafting rate of 0.5-1.2%, and the ethylene-propylene copolymer includes random copolymer and block copolymer. The hydrogenated polystyrene elastomer includes styrene-ethylene-butylene-styrene block copolymer (SEBS) and styrene-ethylene-propylene-styrene block copolymer (SEPS).

[0008] Further, the thickness of the polyolefin heat-seal layer is 2-8 μm; And / or, the thickness of the easy-to-peel layer is 8-11 μm; And / or, the thickness of the core layer is 4-30 μm; And / or, the thickness of the composite layer is 5-20 μm.

[0009] Further, the opening smooth master batch in the heat-seal layer is prepared by compounding erucic amide and silicon dioxide, and the carrier thereof is polyolefin.

[0010] As an explanatory description, the opening smooth master batch uses low-density polyethylene or linear low-density polyethylene as the carrier, and is loaded with at least one of erucic amide and silicon dioxide. The mass ratio of erucic amide to silicon dioxide when compounded is preferably 5-15:1.

[0011] Further, the easy-to-peel layer is composed of 50-95 wt% of hydrogenated polystyrene elastomer, 0-45 wt% of polybutene and 5 wt% of maleic anhydride grafted polypropylene.

[0012] Further, the easy-to-peel layer further includes 1-3% of mercaptan compound and 0.3-1% of photoinitiator by weight percentage.

[0013] In the second aspect, the application further provides a preparation method of the composite film with any at least one of the technical features described above, which comprises the following steps: S1: mixing raw materials of the polyolefin heat-seal layer with opening smooth master batch, melt blending through a double-screw extruder, and then casting into a film through a T-shaped die head; S2: melt mixing raw materials of the easy-to-peel layer, and then coating the easy-to-peel layer on the heat-seal layer through an extruder with a casting die head; S3: melt mixing raw materials of the core layer, and then coating the core layer between the corona surface of the composite layer and the easy-to-peel layer through an extruder with a casting die head, and then connecting the composite layer and the easy-to-peel layer through the core layer by a compounding roller.

[0014] Further, In the S1, the twin-screw extruder is melt blended at 180-220℃, and the T-shaped die is cast at a flow rate of 2.5 m / min; Further, in the S2, the melt mixing is carried out at a temperature of 160-190℃, and the die lip temperature of the casting die is 195℃. Further, in the S3, the melt mixing is carried out at a temperature of 210-230℃, and the surface tension of the corona-treated composite layer can reach 40 dyne / cm 2 .

[0015] The composite roll pressure is set to 4-7 bar. When the pressure is less than 3 bar, the bonding force between the core layer and the composite layer is insufficient, and when the pressure is greater than 7 bar, the core layer is excessively penetrated, resulting in an increase in the easy-to-peel layer rigidity.

[0016] Further, in the S2, the melt mixing is carried out under nitrogen protection, the raw materials of the easy-to-peel layer include a mercaptan compound and a photoinitiator, and the easy-to-peel layer is coated on the heat-seal layer and then immediately subjected to UV irradiation treatment.

[0017] Further, the parameters of the UV irradiation treatment include that the UV intensity is 750-850 mJ / cm 2 , and the irradiation time is 3-5 s. The UV irradiation adopts a medium-pressure mercury lamp, the wavelength 365 nm lamp tube is set at a distance of 12 cm from the film surface, and the irradiation intensity is calibrated by an ultraviolet energy meter.

[0018] In a third aspect, the application also relates to a sealing layer of a packaging product connected by heat sealing, self-sealing or the like mode using the composite film.

[0019] The application has the following advantages and beneficial effects: 1. The composite film can withstand high-temperature cooking at 135-141℃ for 40 min, and after cooking, the composite film has a smooth appearance without wrinkles and bubbles. When peeled off, the interface trace of the heat-seal layer is clearly visible, and the peeling area is uniformly white without stringing phenomenon. The heat-seal strength is stable and does not change greatly with the heat-seal temperature, pressure and time, and the easy-to-peel force can be adjusted by adjusting the component ratio in the easy-to-peel layer.

[0020] 2. The mercaptan compound and the unsaturated double bond in the polybutene are triggered by the light-induced click reaction to form a three-dimensional interpenetrating network structure, thereby improving the thermal stability. At the same time, the crosslinked network inhibits the molecular chain slipping, so that the easy-to-peel force fluctuation range is controlled within ±5 N / 15 mm, and the preparation method is seamlessly connected with the casting coating process, thereby realizing online synchronous forming of the multi-layer structure. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a structural schematic diagram of the steam-resistant easy-peel composite film of the present application; Figure 2 is a process flow diagram for preparing the steam-resistant easy-peel composite film of the present application. DETAILED DESCRIPTION

[0022] The present application provides a steam-resistant easy-peel composite film, which has a structure comprising a polyolefin heat-seal layer, an easy-peel layer, a core layer, and a composite layer. The polyolefin heat-seal layer is selected from polypropylene materials and is added with a mustard amide + silica composite opening smooth master batch to ensure the heat-seal strength while avoiding adhesion after steaming through surface lubricity. The easy-peel layer is provided with elastic support by hydrogenated polystyrene elastomer, the peeling force is adjusted by polybutene, and the interface bonding with the heat-seal layer is enhanced by maleic anhydride grafted polypropylene. The core layer is made of high crystallinity polypropylene or olefin copolymer to provide mechanical support and block water vapor penetration. The composite layer is subjected to corona treatment to enhance the adhesion with the substrate such as metal cans / totes, and at the same time, the composite layer itself can be used for printing text, advertisements, and the like.

[0023] The polar groups of the maleic anhydride grafted polypropylene at the interface between the heat-seal layer and the easy-peel layer form a "weak bond" with the non-polar polyolefin of the heat-seal layer, realizing controllable peeling and stable interface after steaming. The core layer material penetrates into the micro-pores of the easy-peel layer and the composite layer after melting, forming physical anchoring and avoiding delamination.

[0024] The peeling performance of the easy-peel layer is provided by the elastic skeleton of the hydrogenated polystyrene elastomer, and the higher the content, the greater the peeling force. The addition of polybutene as a plasticizer will reduce the modulus of the elastomer, thereby reducing the peeling force. The maleic anhydride grafted polypropylene enhances the interface bonding with the heat-seal layer, reduces the delamination phenomenon, and at the same time balances the easy-peeling force value caused by excessive adhesion.

[0025] As a preferred embodiment, in the easy-peel layer, a cross-linked network is formed by the treatment method of thiol compound and photoinitiator cooperating with UV irradiation to inhibit molecular chain slipping at high temperature, further stabilizing the easy-peeling force.

[0026] The present application also provides a preparation method of the above-mentioned composite film, which ensures the fusion bonding of each layer by step-by-step extrusion coating to avoid air bubbles between the layers. After coating the easy-peel layer, high-intensity UV irradiation is immediately performed to trigger the thiol-double bond click reaction, forming a three-dimensional cross-linked network to improve the heat resistance and lock the easy-peeling force value. The surface of the composite layer is subjected to corona treatment to generate oxygen-containing polar groups to improve the composite strength with external substrates.

[0027] Unless otherwise specified, the thiol compound used in the present application is pentaerythritol tetra(3-mercaptopropionate), and the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone. The thiol group (-SH) in the thiol compound and the unsaturated double bond in the polybutene trigger the thiol-alkene click reaction through UV irradiation to form a cross-linked network.

[0028] The specific embodiments of the present application are further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0029] Example 1: A boiling-resistant easy-to-peel composite film comprises a polyolefin heat-seal layer, an easy-to-peel layer, a core layer and a composite layer arranged in sequence. Wherein: The polyolefin heat-seal layer has a thickness of 2 μm and is made of 97% of modified polypropylene and 3% of opening smooth masterbatch; the easy-to-peel layer has a thickness of 9 μm and is made of 95% of hydrogenated polystyrene elastomer by weight and 5% of maleic anhydride grafted polypropylene; the core layer has a thickness of 3 μm and is made of polypropylene; and the composite layer has a thickness of 4 μm and is made of polypropylene film subjected to corona treatment to make the surface tension reach 40 dyne / cm. 2 The polyolefin heat-seal layer has a thickness of 2 μm and is made of 97% of modified polypropylene and 3% of opening smooth masterbatch; the easy-to-peel layer has a thickness of 9 μm and is made of 95% of hydrogenated polystyrene elastomer by weight and 5% of maleic anhydride grafted polypropylene; the core layer has a thickness of 3 μm and is made of polypropylene; and the composite layer has a thickness of 4 μm and is made of polypropylene film subjected to corona treatment to make the surface tension reach 40 dyne / cm.

[0030] The preparation method comprises the following steps: S1: The raw materials of the polyolefin heat-seal layer and the opening smooth masterbatch are mixed in proportion and put into the hopper of the double-screw extruder, and the double-screw extruder melts and blends the raw materials at 200 ℃, and then the film is cast by the T-shaped die at a flow rate of 2.5 m / min; S2: The raw materials of the easy-to-peel layer are melted and mixed in the mixer at 185 ℃, and then coated on the heat-seal layer by the extruder with a casting die, and the die lip temperature of the casting die is 195 ℃; S3: The raw materials of the core layer are melted and mixed in the extruder at 210 ℃, and then the core layer is coated between the corona surface of the composite layer and the easy-to-peel layer by the extruder with a casting die, and the composite layer and the easy-to-peel layer are integrated through the core layer after being pressed by the composite roller at a pressure of 5 bar.

[0031] Example 2: A boiling-resistant easy-to-peel composite film comprises a polyolefin heat-seal layer, an easy-to-peel layer, a core layer and a composite layer arranged in sequence. Wherein: The polyolefin heat-seal layer has a thickness of 5 μm and is made of 98% of ethylene-propylene copolymer and 2% of opening smooth masterbatch (erucamide:silica = 10:1, carrier is linear low density polyethylene); the easy-to-peel layer has a thickness of 10 μm and is made of 67.7 wt% of hydrogenated polystyrene elastomer (SEBS), 25 wt% of polybutene, 5 wt% of maleic anhydride grafted polypropylene, 2% of thiol compound and 0.3% of photoinitiator; the core layer has a thickness of 15 μm and is made of ethylene-hexene copolymer; and the composite layer has a thickness of 12 μm and is made of polyethylene film subjected to corona treatment to make the surface tension reach 45 dyne / cm. 2 The polyolefin heat-seal layer has a thickness of 5 μm and is made of 98% of ethylene-propylene copolymer and 2% of opening smooth masterbatch (erucamide:silica = 10:1, carrier is linear low density polyethylene); the easy-to-peel layer has a thickness of 10 μm and is made of 67.7 wt% of hydrogenated polystyrene elastomer (SEBS), 25 wt% of polybutene, 5 wt% of maleic anhydride grafted polypropylene, 2% of thiol compound and 0.3% of photoinitiator; the core layer has a thickness of 15 μm and is made of ethylene-hexene copolymer; and the composite layer has a thickness of 12 μm and is made of polyethylene film subjected to corona treatment to make the surface tension reach 45 dyne / cm.

[0032] The preparation method comprises the following steps: S1: ethylene-propylene copolymer and opening smooth masterbatch were mixed and put into the hopper of a twin-screw extruder, the raw materials were melt blended at 210°C, and then cast into a film at a flow rate of 2.5 m / min through a T-shaped die; S2: under the protection of nitrogen, the easy-to-open layer raw materials were melt mixed in a mixer at 175°C, and then coated on the heat-seal layer through an extruder with a casting die, immediately irradiated with UV of 800 mJ / cm 2 for 4 s; S3: the core layer raw materials were melt mixed in an extruder at 220°C, and then coated between the corona surface of the composite layer and the easy-to-open layer through an extruder with a casting die, and then combined into one body after being pressed by a composite roller at a pressure of 6 bar.

[0033] Example 3: A boiling-resistant easy-to-open composite film, comprising a polyolefin heat-seal layer, an easy-to-open layer, a core layer and a composite layer arranged in sequence. Among them: The polyolefin heat-seal layer has a thickness of 8 μm and is made of 94% ethylene-propylene copolymer and 6% opening smooth masterbatch (erucamide:silica = 8:1, carrier is low-density polyethylene); the easy-to-open layer has a thickness of 8 μm and is made of 46.5 wt% hydrogenated polystyrene elastomer (SEBS), 45 wt% polybutene, 5 wt% maleic anhydride grafted polypropylene, 3% mercaptan compound and 0.5% photoinitiator; the core layer has a thickness of 30 μm and is made of ethylene-hexene copolymer; and the composite layer has a thickness of 20 μm and is made of polyethylene film with a surface tension of 43 dyne / cm 2 .

[0034] The preparation method comprises the following steps: S1: ethylene-propylene copolymer and opening smooth masterbatch were mixed and put into the hopper of a twin-screw extruder, the raw materials were melt blended at 190°C, and then cast into a film at a flow rate of 2.5 m / min through a T-shaped die; S2: under the protection of nitrogen, the easy-to-open layer raw materials were melt mixed in a mixer at 190°C, and then coated on the heat-seal layer through an extruder with a casting die, immediately irradiated with UV of 850 mJ / cm 2 for 5 s; S3: the core layer raw materials were melt mixed in an extruder at 230°C, and then coated between the corona surface of the composite layer and the easy-to-open layer through an extruder with a casting die, and then combined into one body after being pressed by a composite roller at a pressure of 7 bar.

[0035] Example 4: A boiling-resistant easy-to-open composite film, comprising a polyolefin heat-seal layer, an easy-to-open layer, a core layer and a composite layer arranged in sequence. Among them: The polyolefin heat-seal layer has a thickness of 3 μm and is made of 96% ethylene-propylene copolymer and 4% opening smooth masterbatch (erucic amide:silica = 5:1, carrier is linear low density polyethylene); the easy-to-peel layer has a thickness of 11 μm and is made of hydrogenated polystyrene elastomer (SEBS) 76.6 wt%, polybutene 15 wt%, maleic anhydride grafted polypropylene 5 wt%, and 3% thiol compound and 1% photoinitiator; the core layer has a thickness of 4 μm and is made of ethylene-heptene copolymer; and the composite layer has a thickness of 5 μm and is made of biaxially stretched polypropylene film with surface tension reaching 50 dyne / cm after corona treatment. 2 polyolefin elastomer (POE).

[0036] The preparation method comprises the following steps: S1: ethylene-propylene copolymer and opening smooth masterbatch are mixed in the hopper of a double screw extruder at a certain proportion, the raw materials are melt blended at 180℃, and then a film is cast by a T-shaped die at a flow rate of 2.5 m / min; S2: the raw materials of the easy-to-peel layer are melt mixed in a mixer at 160℃ under nitrogen protection, and then coated on the heat-seal layer by an extruder with a casting die, and immediately irradiated by UV with a strength of 750 mJ / cm 2 for 3 s; S3: the raw materials of the core layer are melt mixed in an extruder at 210℃, and then coated between the corona surface of the composite layer and the easy-to-peel layer by an extruder with a casting die, and then combined into one body after being pressed by a composite roller at a pressure of 4 bar.

[0037] Example 5: A boiling-resistant easy-to-peel composite film comprises a polyolefin heat-seal layer, an easy-to-peel layer, a core layer and a composite layer arranged in sequence. Wherein: The polyolefin heat-seal layer has a thickness of 6 μm and is made of 96% ethylene-propylene copolymer and 4% opening smooth masterbatch (erucic amide:silica = 15:1, carrier is low density polyethylene); the easy-to-peel layer has a thickness of 9 μm and is made of polybutene 95 wt% and maleic anhydride grafted polypropylene 5 wt%; the core layer has a thickness of 25 μm and is made of polypropylene / ethylene-heptene copolymer (mass ratio 7:3); and the composite layer has a thickness of 15 μm and is made of biaxially stretched polypropylene film with surface tension reaching 50 dyne / cm 2 after corona treatment.

[0038] The preparation method comprises the following steps: S1: ethylene-propylene copolymer and opening smooth masterbatch are mixed in the hopper of a double screw extruder at a certain proportion, the raw materials are melt blended at 200℃, and then a film is cast by a T-shaped die at a flow rate of 2.5 m / min; S2: After the easy-to-peel layer raw material is melt-kneaded in a mixer at 185°C under nitrogen protection, the material is coated on the heat-seal layer through an extruder with a casting die; S3: After the core layer raw material is melt-kneaded in an extruder at 225°C, the material is coated between the composite layer and the easy-to-peel layer through an extruder with a casting die, and the layers are integrated after being pressed by a composite roller at a pressure of 5.5 bar.

[0039] The technical effect test results of the above examples are shown in the following table. First, the end edges of the composite films obtained in the examples are heat-sealed, and the heat-seal strength is tested according to GB / T 23561 “Heat-seal Strength Test Procedure”. Then, another composite film of the corresponding example is taken as a sample, 100 mL of rice is placed in the sample, and the boiling resistance test is performed according to GB / T 10004 “Packaging Materials - Test Method for Boiling Resistance”. The appearance is observed after the boiling resistance test of each example, then the easy-to-peel layer is opened, the core layer is separated from the heat-seal layer, and the condition of the torn easy-to-peel layer is observed. Another sample of the corresponding example is heat-sealed according to the same heat-sealing process, and the easy-to-peel performance is tested according to ISO 8510-1 “Peel Force Variation Coefficient Test”. As shown in the above table, the heat-seal strength of each example is stable in the range of 10.8-14.8 N / 15 mm at a heat-seal temperature of 130-180°C, all examples pass the boiling test for 35-50 min at 141°C, which is much higher than the prior art of 121-130°C / 30 min. After boiling, all examples have no wrinkles, delamination, and uniform white space. Examples 2 / 3 / 4 trigger the thiol-double bond reaction by UV irradiation to form a three-dimensional network, which inhibits the slipping of molecular chains at high temperatures, which is beneficial to the boiling resistance performance and further stabilizes the easy-to-peel force under different heat-sealing process conditions. The plasticizing effect of polybutene can reduce the peel force, and the molecular chains are locked by photo-crosslinking to avoid performance degradation at high temperatures. In Example 5, no thiol compound and photo-initiator are added, and the easy-to-peel layer does not form a crosslinked network, and the polybutene molecular chains slip during high-temperature boiling, resulting in an easy-to-peel force fluctuation CV value of 3.8%.

[0040] The above description is only a preferred embodiment of the present application, and it should be noted that for ordinary skilled persons in the technical field, several improvements and refinements can be made without departing from the technical principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A heat-resistant and easy-to-peel composite film, characterized in that, It includes a polyolefin heat-sealing layer, an easy-to-peel layer, a core layer, and a composite layer arranged in sequence, with each layer integrally connected by blending blown film or casting coating. The polyolefin heat-sealing layer is made from at least one of polypropylene, modified polypropylene, and ethylene-propylene copolymer, and contains open slip masterbatch accounting for 2-6% of the mass of the polyolefin heat-sealing layer. The easy-peel layer is made of hydrogenated polystyrene elastomer and / or polybutene, and contains 2-10% maleic anhydride-grafted polypropylene by weight of the total mass of the easy-peel layer. The core layer is made of at least one of polypropylene, ethylene-propylene copolymer, ethylene-hexene copolymer, and ethylene-heptene copolymer. The composite layer is made of polyolefin with surface corona treatment.

2. The composite membrane according to claim 1, characterized in that, The thickness of the polyolefin heat-sealing layer is 2-8 μm; And / or, the thickness of the easy-to-remove layer is 8-11 μm; And / or, the thickness of the core layer is 4-30 μm; And / or, the thickness of the composite layer is 5-20 μm.

3. The composite membrane according to claim 1, characterized in that, The open-ended slip masterbatch is prepared by compounding erucamide and silica, and its carrier is polyolefin.

4. The composite membrane according to claim 1, characterized in that, The easy-peel layer is composed of a blend of 50-95 wt% hydrogenated polystyrene elastomer, 0-45 wt% polybutene, and 5 wt% maleic anhydride-grafted polypropylene.

5. The composite membrane according to claim 1, characterized in that, The easy-peel layer also includes 1-3% thiol compounds and 0.3-1% photoinitiator by weight percentage.

6. A method for preparing the composite membrane according to any one of claims 1-5, characterized in that, Includes the following steps: S1: The raw materials for the polyolefin heat-sealing layer are mixed with open slip masterbatch, melt-blended through a twin-screw extruder, and then cast into a film through a T-die. S2: After the raw material of the easy-to-remove layer is melted and mixed, it is coated onto the heat-sealing layer through an extruder with a casting die; S3: After the raw materials of the core layer are melted and mixed, the core layer is coated between the corona surface of the composite layer and the easy-to-peel layer through an extruder with a casting die. The composite layer and the easy-to-peel layer are then connected as one through the core layer by the composite roller.

7. The preparation method according to claim 6, characterized in that, In step S1, the melt blending temperature of the twin-screw extruder is 180-220℃, and the T-die casting speed is 2.5m / min. And / or the melt mixing temperature in step S2 is 160-190℃, and the die lip temperature of the casting die head is 195℃; And / or the melting and mixing temperature in step S3 is 210-230℃.

8. The preparation method according to claim 6, characterized in that, In step S2, the melt mixing is carried out under nitrogen protection, and the easy-peel layer is applied to the heat-sealing layer and then immediately subjected to UV irradiation treatment with an irradiation intensity of 750-850 mJ / cm. 2 The irradiation time is 3-5 seconds.

9. The preparation method according to claim 6, characterized in that, The surface tension of the composite layer after corona treatment is 40 dyne / cm. 2 .

10. An application of the composite membrane according to any one of claims 1-5, characterized in that, Packaging materials that are joined by heat sealing or self-sealing, including metal cans, trays or stand-up pouches, and used for packaging cooked food, high-temperature prepared dishes or milk powder.

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