High-temperature retort lidding easy-open film and method of making same

Abstract

The application relates to the field of high polymer materials, and particularly discloses a high-temperature cooking cover easy-to-rip film and a preparation method thereof. The high-temperature cooking cover easy-to-rip film comprises an outer layer, a middle layer and an inner layer in sequence, and the inner layer comprises the following raw materials: high-density polyethylene, ethylene-butene copolymer, PPA additive, linear low-density polyethylene, slip agent and polypropylene; the middle layer comprises the following raw materials: metallocene ultra-low-density polyethylene, high-density polyethylene, linear low-density polyethylene and metallocene linear low-density polyethylene; and the outer layer comprises the following raw materials: high-density polyethylene, linear low-density polyethylene and polypropylene. The high-temperature cooking cover easy-to-rip film has the advantages that no delamination phenomenon occurs after cooking at 125 DEG C for 30 min, the heat sealing window is wide, the heat sealing strength is moderate, the seal is easy to tear, the film is smooth and has no abrupt feeling when being ripped, the barrier property and the anti-pollution property are good, and the product has a longer shelf life.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and more specifically, it relates to a high-temperature cooking and sealing easy-to-remove film and its preparation method. Background Technology

[0002] Easy-open film materials have been widely used in various packaging applications. For example, they are used to directly process various packaging bags or as lids for bowl-shaped, cup-shaped, barrel-shaped, and box-shaped containers made of PP material. Packaging products prepared by combining easy-open lid film with block copolymer PP material containers can replace glass bottles, jars, and tin cans, which consume a lot of energy, have high storage and transportation costs, and occupy a lot of space.

[0003] Because canned fruits, meats, fish, and porridge require sterilization at 110℃~121℃ for half an hour to an hour during production, traditional composite flexible packaging technology combining easy-open lid film with block copolymer PP cups is mainly used in the packaging of processed foods such as room-temperature or low-temperature jellies, yogurts, and puddings. This combination of lid film and block copolymer PP cups cannot withstand high-temperature heating, and after high-temperature heating, problems such as poor sealing and poor barrier properties against contamination easily occur.

[0004] In the prior art, Chinese invention patent application CN113427871 discloses an easy-to-peel film material that can withstand high-temperature cooking. It is co-extruded from a corona layer, an intermediate layer, and a heat-sealing layer. The corona layer material is metallocene block copolymer PP or a mixture of metallocene medium-density polyethylene and high-density polyethylene; the intermediate layer material is metallocene high-density polyethylene; the heat-sealing layer material is copolymerized from high-density polyethylene (HDPE), block copolymer PP (PP), and polybutene (PB). Although it can withstand high-temperature cooking at 121℃ / 30min, the heat-sealing layer is co-extruded from PE and PP, which have poor compatibility. It is easy to string when peeling, and the peeling marks are rough and the peeling surface is damaged. This makes it easy for the film to tear at the damaged area and remain on the container, making it difficult to peel off the cover completely.

[0005] Regarding the aforementioned technologies, the inventors discovered that while current easy-open lid films can heat-seal PP cups, they are not resistant to steaming or boiling, and the heat-sealed area easily opens after steaming or boiling. Alternatively, while they may meet the requirements for high-temperature steaming, they are not easy to peel off completely, and residue or stringing is common. Summary of the Invention

[0006] To simultaneously achieve the effects of high-temperature cooking resistance and easy opening, this application provides a high-temperature cooking sealing film with easy opening and its preparation method.

[0007] In the first aspect, this application provides a high-temperature cooking and sealing easy-to-remove film, which adopts the following technical solution:

[0008] A high-temperature retort sealing and easy-open film, comprising an outer layer, a middle layer, and an inner layer from the outside to the inside, wherein the inner layer comprises the following raw materials in parts by weight: 25-35 parts high-density polyethylene, 15-25 parts ethylene-butene copolymer, 0.6-1 part PPA additive, 25-35 parts linear low-density polyethylene, 1.5-2.5 parts slip agent, 15-25 parts polypropylene, and 2-2.8 parts opening agent;

[0009] The middle layer comprises the following raw materials in parts by weight: 25-35 parts metallocene ultra-low density polyethylene, 25-35 parts high density polyethylene, 15-25 parts linear low density polyethylene, 15-25 parts metallocene linear low density polyethylene, and 0.6-1 parts PPA additive.

[0010] The outer layer comprises the following raw materials in parts by weight: 35-45 parts high-density polyethylene, 35-45 parts linear low-density polyethylene, 15-25 parts polypropylene, and 0.6-1 parts PPA additive.

[0011] By adopting the above technical solution, HDPE and linear low-density polyethylene are used in the outer and inner layers, combined with polypropylene in the above proportions, a high temperature resistance effect is achieved. It will not open after being boiled at 125°C for 30 minutes, and a stable heat-sealing effect can be achieved, resulting in easy tearing and high temperature resistance. Although polypropylene is added to the inner and outer layers, the inner layer contains ethylene-butene copolymer, and two different metallocene linear low-density polyethylenes are added to the middle layer, which can improve the compatibility of the raw materials, achieve tight bonding between layers, and prevent delamination and stringing when peeling off the film.

[0012] Optionally, the layers are arranged from the outside to the inside as an outer layer, a middle layer, and an inner layer, wherein the inner layer comprises the following raw materials in parts by weight: 30-35 parts high-density polyethylene, 15-20 parts ethylene-butene copolymer, 0.6-0.8 parts PPA additive, 25-30 parts linear low-density polyethylene, 1.5-2 parts slip agent, 15-20 parts polypropylene, and 2-2.4 parts opening agent;

[0013] The middle layer comprises the following raw materials in parts by weight: 30-35 parts metallocene ultra-low density polyethylene, 30-35 parts high density polyethylene, 20-25 parts linear low density polyethylene, 20-25 parts metallocene linear low density polyethylene, and 0.8-1 parts PPA additive.

[0014] The outer layer comprises the following raw materials in parts by weight: 40-45 parts high-density polyethylene, 40-45 parts linear low-density polyethylene, 20-25 parts polypropylene, and 0.8-1 parts PPA additive.

[0015] By adopting the above technical solution, the amount of raw materials used in the outer, middle and inner layers can be more precise, and better high temperature resistance, easy peeling and heat sealing effects can be achieved.

[0016] The polypropylene in the inner and outer layers is selected from block copolymer PP, random copolymer PP, and homopolymer PP.

[0017] By adopting the above technical solutions, block copolymer PP, random copolymer PP, and homopolymer PP are used in the inner and outer layers to improve the impact resistance and tear resistance of the easy-peel film.

[0018] Optionally, the block copolymer PP in the inner and outer layers has a melt index of 2.5-3.5 g / 10 min and a density of 0.9-1 g / cm³. 3 .

[0019] By adopting the above technical solutions, the block copolymer PP with the above density and melt index has high impact resistance, good heat resistance, and can improve the impact resistance and boiling resistance of easy-to-peel film.

[0020] Optionally, the melt index of the random copolymer PP in the inner and outer layers is 9.5-10 g / 10 min, and the density is 0.9-0.94 g / cm³. 3 .

[0021] By adopting the above technical solutions, the random copolymer PP with the above melt index and density has high tensile strength, high heat distortion temperature, and good heat resistance.

[0022] Optionally, the homopolymer PP in the inner and outer layers has a melt index of 0.5-1 g / 10 min and a density of 0.9-0.95 g / cm³. 3 .

[0023] By adopting the above technical solutions, homopolymer PP with the above density and melt index has good heat resistance, high mechanical strength and good wear resistance, and can improve the mechanical strength and heat resistance of easy-to-peel film.

[0024] Optionally, the linear low-density polyethylene in the outer, middle, and inner layers has a density of 0.90-0.94 g / cm³. 3 The melt flow index is 0.9-1.2 g / 10 min.

[0025] By adopting the above technical solution, this linear low-density polyethylene with high density and melt index has a high softening temperature and melting temperature, high strength, good toughness, high rigidity, heat resistance, cold resistance, and good resistance to environmental stress cracking, impact strength, and tear strength. When used in combination with high-density polyethylene and polypropylene, it can improve the heat resistance and easy-to-peel effect of the easy-peel film.

[0026] Optionally, the density of the intermediate layer of metallocene linear low-density polyethylene is 0.94-0.95 g / cm³. 3The melt flow index is 0.9-1 g / 10 min.

[0027] By adopting the above technical solution, the metallocene low-density polyethylene in the middle layer has a low melt index, which can improve the compatibility between the high-density polyethylene and linear low-density polyethylene in the middle layer and the high-density polyethylene, PP and linear low-density polyethylene in the outer and inner layers, and prevent crystal points, lumps and delamination from appearing in the easily peelable film.

[0028] Optionally, the density of the high-density polyethylene in the inner and outer layers is 0.956-0.96 g / cm³. 3 The melt flow index is 1.0-1.2 g / 10 min;

[0029] The density of the high-density polyethylene in the middle layer is 0.946-0.95 g / cm³. 3 The melt flow index is 6-6.5 g / 10 min.

[0030] By adopting the above technical solution, the high-density polyethylene selected in the inner and outer layers has a high heat distortion temperature and good heat resistance, belonging to high heat-resistant HDPE materials, which can improve the heat resistance of the easy-to-peel film; the middle layer uses high-density polyethylene with a slightly lower heat distortion temperature, which has a high flow rate, large molecular weight, and good mechanical properties.

[0031] Optionally, the density of the metallocene ultra-low density polyethylene in the middle layer is 0.916-0.92 g / cm³. 3 The melt flow index is 0.5-1 g / 10 min.

[0032] By adopting the above technical solutions, metallocene ultra-low density polyethylene with the above density and melt index has contact tensile strength, impact resistance and puncture resistance.

[0033] Optionally, antioxidants are added to the outer layer, inner layer and middle layer, and the amount of antioxidants used is 0.5-1 parts by weight.

[0034] By adopting the above technical solution, antioxidants can prevent excessive polymerization, oxidation, and charring of the film surface under high temperature conditions, thus preventing crystal points and paste from appearing on the film surface, improving processing performance, and improving the appearance quality of the product.

[0035] Secondly, this application provides a method for preparing a high-temperature cooking and sealing easy-to-remove film, which adopts the following technical solution:

[0036] A method for preparing a high-temperature cooking and easy-to-remove sealing film includes the following steps:

[0037] The raw materials for the outer, middle, and inner layers are mixed evenly, then heated and melted, extruded, blown and cooled, drawn and shaped, corona treated, and wound up.

[0038] By adopting the above technical solution, cold air at a temperature of 0-5℃ is used for air cooling, which improves the stability of the membrane bubble.

[0039] Optionally, the following post-processing steps are also included: coating the outer layer of the obtained high-temperature retort sealing easy-open film with a mixed emulsion containing graphene, epoxy resin and polyamide, and after drying, placing the side of the high-temperature retort sealing easy-open film coated with the mixed emulsion on top of PFDS, and vacuum evaporating for 30-35 minutes at 100-110℃ and 60-70kPa.

[0040] By adopting the above technical solution, the barrier ability of easy-open film to water and oxygen affects the shelf life of food when packaging it. Therefore, the manufactured easy-open film is post-processed by first coating the outer layer with a layer of epoxy resin emulsion containing graphene. The layered structure of graphene can prolong the permeation path of water vapor and oxygen, reduce the amount of water vapor and oxygen permeation, and improve the barrier properties. Meanwhile, the vacuum evaporation of PDFS on the outer layer can provide a higher fluorine density to the outer layer, reduce the surface free energy of the outer layer, improve its hydrophobicity, increase the permeation resistance of water vapor, and improve the barrier ability of water vapor.

[0041] In summary, this application has the following beneficial effects:

[0042] 1. Because this application uses high-temperature resistant high-density polyethylene and high-density linear low-density polyethylene and PP in combination, by adjusting the amount of each raw material, it achieves easy-to-peel film with moderate temperature resistance and heat sealing strength, easy to tear open, smooth tear marks without stringing, and can realize the industrial processing of blown film, ensuring the product quality of blown film.

[0043] 2. In this application, metallocene linear low-density polyethylene with a low melt index is preferably used in the middle layer, which can improve the compatibility of high-density polyethylene, linear low-density polyethylene and other materials with the raw materials in the outer and inner layers, making the film layer less prone to delamination, less prone to crystal points and lumps, and improving the appearance quality of the easy-to-peel film.

[0044] 3. In this application, it is preferred to coat the outer layer of the easy-open film with an epoxy resin emulsion containing graphene, and then perform vacuum evaporation of PDFS to achieve barrier modification of the outer film, improve the water and oxygen barrier effect of the easy-open film, and improve the food storage capacity of the easy-open film. Detailed Implementation

[0045] Example

[0046] Table 1. Sources of raw materials in the high-temperature cooking and easy-open sealing film.

[0047]

[0048]

[0049] Example 1: A high-temperature retort sealing and easy-open film, comprising an outer layer, a middle layer, and an inner layer. The raw material sources for each layer are shown in Table 1, and the raw material quantities are shown in Table 2. The inner layer raw materials in Table 2 have a melt index (190℃ / 2.16kg) of 1g / 10min and a density of 0.956g / cm³. 3 The product, model F920A, is a linear low-density polyethylene with a melt index (190℃ / 2.16kg) of 1 g / 10min and a density of 0.92 g / cm³. 3 The product model is SP3210. The polypropylene is a block copolymer PP. The melt index (230℃ / 2.16kg) of the block copolymer PP is 2.5g / 10minL, and the density is 0.9g / cm³. 3 The model number is K8003; the density of the raw materials in the middle layer is 0.916 g / cm³, which is metallocene ultra-low density polyethylene. 3 The melt flow index (190℃ / 2.16kg) is 0.5g / 10min, and the model number is X8656; the density of high-density polyethylene is 0.946g / cm³. 3 The melt flow index (190℃ / 2.16kg) is 6 g / 10min; the melt flow index (190℃ / 2.16kg) of linear low-density polyethylene is 1.9 g / 10min, and the density is 0.925 g / cm³. 3 The model number is SP2520, and the density of the metallocene linear low-density polyethylene is 0.94 g / cm³. 3 The melt flow index (190℃ / 2.16kg) is 0.9g / 10min, and the model number is 4009MC; the outer layer materials are: high-density polyethylene with a melt flow index (190℃ / 2.16kg) of 1g / 10min and a density of 0.956g / cm³. 3 The product, model F920A, is a linear low-density polyethylene with a melt index (190℃ / 2.16kg) of 1 g / 10min and a density of 0.92 g / cm³. 3 The product model is SP3210. The polypropylene is a block copolymer PP. The melt index (230℃ / 2.16kg) of the block copolymer PP is 2.5g / 10minL, and the density is 0.9g / cm³. 3 The model number is K8003.

[0050] The above-mentioned method for preparing the high-temperature cooking and easy-to-remove sealing film includes the following steps:

[0051] The raw materials for the outer, middle, and inner layers are mixed evenly and fed into the outer, middle, and inner layer extruders respectively for heating and melting. The molten adhesive is then conveyed to the die head for extrusion blow molding to obtain a film bubble. After being cooled by air cooling, the film bubble is traction-shaped and then enters the corona treatment device through guide rollers for corona treatment. After winding, a high-temperature retort sealing easy-open film with a thickness of 70μm is obtained. The temperatures of each zone of the extruder are shown in Table 3. The cold air temperature is 5℃, and the screw speed is 52r / min for the middle layer, 45r / min for the inner layer, and 45r / min for the outer layer.

[0052] Table 2. Raw material usage for high-temperature cooking and easy-to-remove sealing film in Examples 1-6

[0053]

[0054] Table 3 Temperatures in the outer, inner, and middle zones of the extruder

[0055]

[0056]

[0057] Examples 2-6: A high-temperature cooking and sealing film with easy-to-remove coating, which differs from Example 1 in that the amount of raw materials used is shown in Table 2.

[0058] Example 7: A high-temperature retort sealing and easy-open film, differing from Example 1 in that the polypropylene in the inner and outer layers is random copolymer PP with a melt index of 10 g / 10 min and a density of 0.9 g / cm³. 3 The model number is AW564G.

[0059] Example 8: A high-temperature retort sealing and easy-open film, differing from Example 1 in that the polypropylene in both the inner and outer layers is homopolymer PP with a melt index of 0.5 g / 10 min and a density of 0.9 g / cm³. 3 The model number is 1005.

[0060] Example 9: A high-temperature retort sealing easy-open film, which differs from Example 1 in that the prepared high-temperature retort sealing easy-open film undergoes the following post-treatment: a mixed emulsion containing 1 kg graphene, 2 kg epoxy resin, 1 kg polyamide and 3.7 kg xylene is coated on the outer layer of the high-temperature retort sealing easy-open film, dried, and the side of the high-temperature retort sealing easy-open film coated with the mixed emulsion is placed on top of PFDS, and vacuum evaporated for 30 min at 100°C and 70 kPa.

[0061] Example 10: A high-temperature retort sealing easy-open film, which differs from Example 1 in that the high-temperature retort sealing easy-open film is subjected to the following post-treatment: a mixed emulsion containing 1 kg graphene, 2 kg epoxy resin, 1 kg polyamide and 3.7 kg xylene is coated on the outer layer of the high-temperature retort sealing easy-open film, and then dried.

[0062] Example 11: A high-temperature retort sealing easy-open film, which differs from Example 1 in that the prepared high-temperature retort sealing easy-open film is subjected to the following post-treatment: the outer layer of the high-temperature retort sealing easy-open film is placed on top of PFDS and vacuum evaporated for 30 minutes at 100°C and 70 kPa.

[0063] Comparative Example

[0064] Comparative Example 1: A high-temperature cooking and sealing easy-open film, which differs from Example 1 in that it uses an equal amount of high-density polyethylene in the middle layer to replace the high-density polyethylene in the outer layer.

[0065] Comparative Example 2: A high-temperature cooking and sealing easy-open film, differing from Example 1 in that it uses a material with a mass density of 0.918 g / cm³. 3 MLLDPE with a melt index (190℃ / 2.16kg) of 3.5g / 10min replaces linear low-density polyethylene in the outer layer.

[0066] Comparative Example 3: A high-temperature cooking and easy-to-open sealing film, which differs from Example 1 in that high-density polyethylene is not added to the inner layer.

[0067] Comparative Example 4: A high-temperature cooking and easy-to-open sealing film, which differs from Example 1 in that no linear low-density polyethylene is added to the inner layer.

[0068] Comparative Example 5: A high-temperature cooking and easy-to-open sealing film, which differs from Example 1 in that no polypropylene is added to the inner layer.

[0069] Comparative Example 6: A high-temperature cooking and easy-to-open sealing film, which differs from Example 1 in that the inner layer does not contain ethylene-butene copolymer.

[0070] Comparative Example 7: A high-temperature cooking and easy-to-open sealing film, which differs from Example 1 in that no metallocene linear low-density polyethylene is added to the middle layer.

[0071] Comparative Example 8: A high-temperature cooking and easy-to-open sealing film, which differs from Example 1 in that linear low-density polyethylene SP3210 is used in an equal amount to replace metallocene linear low-density polyethylene in the middle layer.

[0072] Comparative Example 9: A high-temperature resistant, easy-to-peel film material, co-extruded from a corona layer, an intermediate layer, and a heat-sealing layer, with a mass ratio of 7:10:3. The corona layer material is a mixture of 50 wt% metallocene medium-density polyethylene and 50 wt% high-density polyethylene; the intermediate layer material is metallocene high-density polyethylene; the heat-sealing layer material is a copolymer of high-density polyethylene (HDPE), polypropylene (PP), and polybutene (PB1); the density of the metallocene medium-density polyethylene is 0.934 g / cm³. 3 The melt flow index is 0.9 g / 10 min; the density of the high-density polyethylene is 0.961 g / cm³. 3 The melt flow index is 0.85 g / 10 min; the melt flow index of the metallocene high-density polyethylene is 0.7 g / 10 min.

[0073] Performance testing

[0074] I. Mechanical strength and heat-sealing performance testing: The high-temperature cooking and sealing easy-open film was prepared according to the above method, and the performance of the easy-open film was tested according to the following methods. Three groups of samples were tested for each performance, and the average value was taken. The test results were recorded in Tables 4, 5 and 6.

[0075] 1. Tensile strength: Tested in accordance with GB / T13022-1991 "Test Method for Tensile Properties of Plastic Films";

[0076] 2. Elongation at break: Tested according to GB / T13022-1991 "Test Method for Tensile Properties of Plastic Films";

[0077] 3. Tear strength: Tested according to GB / T16578-1996 "Test method for tear resistance of plastic films and sheets";

[0078] 4. Heat seal strength: Tested according to QB-T2358 "Test Method for Heat Seal Strength of Plastic Packaging";

[0079] 5. Heat seal strength with PP cup body (0.2MPa, 1s) and opening marks: Test according to QB-T2358 "Test method for heat seal strength of plastic packaging", and open the easy-open film to observe the easy-open film and opening marks;

[0080] 6. Oil bath test: Fold the prepared easy-peel film so that the inner layers are in contact with each other, place it directly in silicone oil, heat it, keep it at that temperature for 30 minutes, and observe whether the easy-peel film sticks or shrinks.

[0081] Table 4 Performance testing of the high-temperature resistant easy-open capping films prepared in Examples 1-6

[0082]

[0083]

[0084] As can be seen from the data in Table 4, the easy-open films prepared in Examples 1-6 do not shrink or stick when kept in an oil bath at 125°C for 30 minutes, and only slightly stick when kept in an oil bath at 130°C for 30 minutes. They have high high-temperature resistance and can maintain strong physical properties after heating when used for sealing PP cups. Moreover, the heat seal strength with the PP cup is not high, and they are easy to open.

[0085] Table 5 Performance testing of the easy-peel films prepared in Examples 8-11 and Comparative Examples 1-3

[0086]

[0087]

[0088] As can be seen from the data in Table 5, the easy-peel film made by random copolymer PP in Example 7 has slightly lower mechanical strength and slightly weaker heat resistance compared with Example 1; the easy-peel film made by homopolymer PP in Example 8 has weaker heat resistance compared with Example 1.

[0089] In Examples 9-11, post-treatment of the outer layer of the easy-peel film improved the filament strength, elongation at break, and tear strength. In Comparative Example 1, the use of high-density polyethylene with a lower heat deformation temperature in the middle layer instead of high-density polyethylene with a high heat deformation temperature in the outer layer resulted in a decrease in the heat resistance of the easy-peel film, which was prone to adhesion and shrinkage under high-temperature cooking. In Comparative Example 2, the use of lower-density metallocene linear low-density polyethylene resulted in a slight decrease in the tensile strength and other mechanical properties of the easy-peel film, and a weakening of its resistance to high-temperature cooking.

[0090] Table 6 Performance testing of the high-temperature retort-resistant, easy-open capping films prepared in Comparative Examples 3-9

[0091]

[0092]

[0093] Based on the data in Table 6, it can be seen from the data in Table 6 that the inner layer of the easy-open film prepared in Examples 3-6 has weakened heat-sealing strength and significantly reduced heat-sealing strength with the PP cup body, thus failing to guarantee good sealing performance. The mechanical strength of the easy-open film prepared in Comparative Example 6 is also weakened.

[0094] Comparative Example 7 did not add metallocene linear low-density polyethylene to the middle layer, while Comparative Example 8 used linear low-density polyethylene instead of metallocene linear low-density polyethylene. The mechanical properties of the easy-to-peel films prepared in Comparative Example 7 and Comparative Example 8 were smaller than those in Example 1, but their heat-sealing properties did not change much.

[0095] Comparative Example 9 is a heat-resistant and easy-to-peel film prepared by existing technology, but its heat-sealing strength with the PP cup body is relatively large, making it difficult to achieve the effect of easy peeling.

[0096] II. Barrier performance test: The easy-peel films prepared in Examples 1 and 9-11 were tested according to the following method, and the test results are recorded in Table 7.

[0097] 1. Water vapor transmission rate: Tested according to GB / T1037-2021 "Determination of water vapor transmission performance of plastic films and sheets - cup method for weight gain and weight loss";

[0098] 2. Oxygen transmission rate: Tested according to GB / T19789-2021 "Test method for oxygen transmission rate of plastic sheets and films for packaging materials - coulometric method".

[0099] Table 7 Barrier performance tests of the easy-peel films prepared in Examples 7 and 9

[0100]

[0101]

[0102] As can be seen from the data in Table 7, in Example 1, no post-treatment was performed on the outer layer of the easy-open film, and the barrier properties of the easy-open film against water vapor and oxygen need to be improved. In Example 9, the outer layer of the easy-open film was coated with an epoxy resin emulsion containing graphene, and PFDS was deposited by vacuum evaporation. The barrier properties of the easy-open film prepared in Example 7 were improved, which can improve the long-term storage capacity of the easy-open film for food products. In Example 10, only the outer layer of the easy-open film was coated with epoxy resin containing graphene, and its water vapor permeability and oxygen permeability were significantly increased. In Example 11, only vacuum evaporation of PFDS was used. In Example 11, the barrier properties against water vapor were weakened and increased, while the barrier properties against oxygen were also weakened. This shows that post-treatment of the easy-open film can significantly enhance its barrier properties and improve the storage stability of its food packaging.

[0103] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-temperature steaming and sealing easy-to-remove film, characterized in that, From the outside to the inside, the material consists of an outer layer, a middle layer, and an inner layer. The inner layer comprises the following raw materials in parts by weight: 25-35 parts high-density polyethylene, 15-25 parts ethylene-butene copolymer, 0.6-1 part PPA additive, 25-35 parts linear low-density polyethylene, 1.5-2.5 parts slip agent, 15-25 parts polypropylene, and 2-2.8 parts opening agent. The middle layer comprises the following raw materials in parts by weight: 25-35 parts metallocene ultra-low density polyethylene, 25-35 parts high density polyethylene, 15-25 parts linear low density polyethylene, 15-25 parts metallocene linear low density polyethylene, and 0.6-1 parts PPA additive. The outer layer comprises the following raw materials in parts by weight: 35-45 parts high-density polyethylene, 35-45 parts linear low-density polyethylene, 15-25 parts polypropylene, and 0.6-1 parts PPA additive. The polypropylene in the inner and outer layers is block copolymer PP; The linear low-density polyethylene in the outer, middle, and inner layers has a density of 0.90-0.94 g / cm³. 3 The melt flow index is 0.9-1.2 g / 10 min; The density of the high-density polyethylene in the inner and outer layers is 0.956-0.96 g / cm³. 3 The melt flow index is 1.0-1.2 g / 10 min; The density of the middle-layer metallocene linear low-density polyethylene is 0.94-0.95 g / cm³. 3 The melt flow index is 0.9-1 g / 10 min; The density of the high-density polyethylene in the middle layer is 0.946-0.95 g / cm³. 3 The melt flow index is 6-6.5 g / 10 min; The density of the metallocene-containing ultra-low density polyethylene in the middle layer is 0.916-0.92 g / cm³. 3 The melt flow index is 0.5-1 g / 10 min.

2. The high-temperature cooking and sealing easy-open film according to claim 1, characterized in that: From the outside to the inside, the material consists of an outer layer, a middle layer, and an inner layer. The inner layer comprises the following raw materials in parts by weight: 30-35 parts high-density polyethylene, 15-20 parts ethylene-butene copolymer, 0.6-0.8 parts PPA additive, 25-30 parts linear low-density polyethylene, 1.5-2 parts slip agent, 15-20 parts polypropylene, and 2-2.4 parts opening agent. The middle layer comprises the following raw materials in parts by weight: 30-35 parts metallocene ultra-low density polyethylene, 30-35 parts high density polyethylene, 20-25 parts linear low density polyethylene, 20-25 parts metallocene linear low density polyethylene, and 0.8-1 parts PPA additive. The outer layer comprises the following raw materials in parts by weight: 40-45 parts high-density polyethylene, 40-45 parts linear low-density polyethylene, 20-25 parts polypropylene, and 0.8-1 parts PPA additive.

3. The high-temperature cooking and sealing easy-open film according to claim 1, characterized in that, Antioxidants are added to the outer, inner, and middle layers, and the amount of each antioxidant is 0.5-1 parts by weight.

4. The method for preparing the high-temperature cooking and easy-to-open sealing film according to any one of claims 1-3, characterized in that, Includes the following steps: The raw materials for the outer, middle, and inner layers are mixed evenly, then heated and melted, extruded, blown and cooled, drawn and shaped, corona treated, and wound up.

5. The method for preparing the high-temperature cooking and easy-to-open sealing film according to claim 4, characterized in that, The process also includes the following post-processing steps: a mixed emulsion containing graphene, epoxy resin and polyamide is coated on the outer layer of the obtained high-temperature cookable and easy-to-open film. After drying, the side of the high-temperature cookable and easy-to-open film coated with the mixed emulsion is placed on top of the PFDS and vacuum evaporated for 30-35 minutes at 100-110℃ and 60-70kPa.

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