Retortable high function polyethylene film and method for producing the same

Abstract

The application discloses a kind of cooking grade high-function polyethylene film and preparation method thereof, belong to plastic film technical field.The polyethylene film is composed of the following weight parts raw materials: high-density polyethylene 40-60 parts, linear low-density polyethylene 20-40 parts, carboxyl or maleic anhydride modified polyethylene 20-40 parts, epoxy compound 0.5-2 parts, zinc acetate 0.5-1 part, opening agent 1 part and slip agent 1 part.Epoxy compound and carboxyl / anhydride group in modified polyethylene form dynamic covalent crosslinking network under the catalysis of zinc acetate, effectively limit polyethylene molecular chain high temperature movement, inhibit the recrystallization behavior in cooking process.The preparation method includes: raw material premixing, twin-screw extruder melt granulation, film blowing molding.The single-layer film thickness of the application is 50-80 μm, initial haze is less than 20%, after 121 DEG C / 30min cooking, heat shrinkage is less than or equal to 2%, haze change is less than or equal to 2%, without whitening and tackiness phenomenon, solve the performance degradation problem of traditional PE film after high-temperature cooking, while maintaining excellent heat sealability and transparency.

Description

Technical Field

[0001] This invention relates to the field of plastic film technology, and in particular to a retortable high-performance polyethylene film and its preparation method. Background Technology

[0002] Polyethylene (PE) film is widely used in food packaging due to its excellent processability, non-toxicity, chemical stability, and low cost, especially in heat-sealable packaging for products such as jellies, meat products, and convenience foods. However, as food packaging demands increasingly stringent safety and shelf-life requirements, many products require high-temperature sterilization at temperatures above 121°C to achieve commercial sterility and extend shelf life. This places higher demands on the heat resistance of packaging films. Ordinary PE film, with its low melting point, is prone to melting and recrystallization during high-temperature sterilization, leading to film adhesion, deformation, whitening, and even heat-sealing failure, leakage, and other problems, severely impacting packaging sealing and food safety. Therefore, ordinary PE film is ill-suited for long-term high-temperature sterilization and urgently needs modification or structural design to improve its high-temperature resistance, meeting the technical requirements of modern food packaging for high-temperature stability, safety, and reliability.

[0003] To improve the heat resistance of polyethylene films, existing technologies typically employ composite multilayer structures or rigid filler modifications. For example, patent 202110521200.1 discloses a high-temperature retortable PE film prepared by three-layer co-extrusion blow molding, which uses bimodal metallocene medium-density polyethylene (mPE) and high-density polyethylene (HDPE) as the corona layer, intermediate layer, and heat-sealing layer, respectively. However, it mainly relies on changing the proportion of polyethylene components in each layer to improve heat resistance, making the process complex. Another patent, 202310012356.6, proposes adding cage-like polysilsesquioxane (POSS), ethylene-vinyl alcohol copolymer (EVOH), and radiation crosslinking sensitizer to the PE retortable film to enhance the film's rigidity and improve its heat resistance.

[0004] However, rigid fillers and radiation crosslinking can reduce the heat-sealing performance of the film, and rigid fillers are difficult to disperse uniformly, which can increase the haze of the film. In addition, radiation crosslinking requires additional equipment and post-processing, resulting in higher costs. Summary of the Invention

[0005] The present invention aims to provide a cooking-grade high-functionality polyethylene film and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a retortable high-functionality polyethylene film, prepared from raw materials comprising the following parts by weight: 40-60 parts of high-density polyethylene, 20-40 parts of linear low-density polyethylene, 20-40 parts of carboxyl / maleic anhydride modified polyethylene, 0.5-2 parts of epoxy compound, 0.5-1 part of zinc acetate, 1 part of opening agent, and 1 part of slip agent; wherein, the epoxy compound and the active groups in the carboxyl or maleic anhydride modified polyethylene form a reversible dynamic covalent crosslinking network under the catalysis of zinc acetate.

[0007] As a preferred embodiment of the present invention, the density of the high-density polyethylene is 0.955-0.965 g / cm³. 3 The melt flow index is 1-2 g / 10 min; the density of the linear low-density polyethylene is 0.925-0.940 g / cm³. 3 The melt index is 1-2 g / 10 min.

[0008] As a preferred embodiment of the present invention, the carboxyl-modified polyethylene is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer, wherein the content of acrylic acid or methacrylic acid is 3wt%-6wt%; the maleic anhydride-modified polyethylene is maleic anhydride-grafted low-density polyethylene, and the maleic anhydride grafting content is 0.8%-1.2%.

[0009] As a preferred embodiment of the present invention, the epoxy compound is selected from one or more mixtures of epoxidized soybean oil, pentaerythritol glycidyl ether, glycerol triglycidyl ether, butylene glycol diglycidyl ether, and bisphenol A glycidyl ether.

[0010] In a preferred embodiment of the present invention, the opening agent is silica microparticles and the slip agent is a fatty acid amide compound.

[0011] As a preferred embodiment of the present invention, the polyethylene film is a single-layer blown film with a thickness of 50-80 μm.

[0012] A method for preparing a retortable high-performance polyethylene film includes the following steps:

[0013] (a) Premixing: Mix the raw materials in a high-speed mixer for 5-10 minutes according to the weight parts;

[0014] (b) Melt extrusion: Granulation is carried out using a twin-screw extruder at 150-210℃ and cooled by cooling water;

[0015] (c) Blown film forming: The granules obtained in step (2) are melted and extruded by a blown film machine at 170-220℃, with a blow-up ratio of 1.5-3 and a traction speed of 20-30m / min to form a film.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: During the melt blending process, under the catalysis of zinc acetate, the present invention enables carboxyl- or maleic anhydride-modified polyethylene and epoxy compounds to form a reversible dynamic covalent crosslinking network in situ. This network significantly restricts the movement of the polyethylene matrix molecular chains, greatly improving the high-temperature resistance of the film and inhibiting its recrystallization behavior during high-temperature cooking, ensuring that the film remains non-sticky, non-deformed, and non-whitening after cooking at 121°C for 30 minutes. Furthermore, the reversible exchange characteristics of the dynamic covalent bonds endow the film with thermoplasticity at high temperatures and enhance its heat-sealing strength, overcoming the heat-sealing failure and decreased transparency problems caused by traditional irradiation crosslinking or rigid filler modification. In addition, the present invention only requires conventional processes of melt blending and blow molding, enabling large-scale industrial production while balancing high-temperature resistance, heat-sealing performance, transparency, and economy. Detailed Implementation

[0017] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0018] This invention discloses a cooking-grade high-functionality polyethylene film and its preparation method.

[0019] The polyethylene film is prepared from the following raw materials in parts by weight: 40-60 parts of high-density polyethylene, 20-40 parts of linear low-density polyethylene, 20-40 parts of carboxyl / maleic anhydride modified polyethylene, 0.5-2 parts of epoxy compound, 0.5-1 part of zinc acetate, 1 part of opening agent, and 1 part of slip agent; wherein the epoxy compound and the active groups in the carboxyl or maleic anhydride modified polyethylene form a reversible dynamic covalent cross-linked network under the catalysis of zinc acetate.

[0020] Epoxy compounds undergo dynamic covalent cross-linking with carboxyl groups or maleic anhydride groups in modified polyethylene to form a reversible ester bond network structure. This effectively restricts the movement of polyethylene molecular chains at high temperatures, significantly improves the high-temperature resistance of the film, and inhibits recrystallization during high-temperature cooking. This overcomes the defects of traditional polyethylene films, such as easy whitening and inner layer adhesion after cooking. The single-layer film of this invention has a thickness of 50-80μm, an initial haze of <20%, and a heat shrinkage rate of ≤2% and haze change of ≤2% after cooking at 121℃ / 30min. There is no whitening or stickiness. This solves the problem of performance degradation of traditional PE films after high-temperature cooking, while maintaining excellent heat-sealing properties and transparency, making it suitable for high-temperature sterilization packaging of food.

[0021] In this embodiment, the opening agent is silica microparticles; the slip agent is a fatty acid amide compound; the epoxy compound is selected from one or more mixtures of epoxidized soybean oil, pentaerythritol glycidyl ether, glycerol triglycidyl ether, butylene glycol diglycidyl ether, and bisphenol A glycidyl ether; the high-density polyethylene has a density of 0.955-0.965 g / cm³ and a melt index of 1-2 g / 10 min; the linear low-density polyethylene has a density of 0.925-0.940 g / cm³. 3 The melt index is 1-2 g / 10 min; the carboxyl-modified polyethylene is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer, wherein the content of acrylic acid or methacrylic acid is 3wt%-6wt%; the maleic anhydride-modified polyethylene is maleic anhydride-grafted low-density polyethylene, and the maleic anhydride grafting content is 0.8%-1.2%; the polyethylene film is a single-layer blown film with a thickness of 50-80 μm.

[0022] A method for preparing a retortable high-performance polyethylene film includes the following steps:

[0023] (a) Premixing: Mix the raw materials in a high-speed mixer for 5-10 minutes according to the weight parts;

[0024] (b) Melt extrusion: Granulation is carried out using a twin-screw extruder at 150-210℃ and cooled by cooling water;

[0025] (c) Blown film forming: The granules obtained in step (2) are melted and extruded by a blown film machine at 170-220℃, with a blow-up ratio of 1.5-3 and a traction speed of 20-30m / min to form a film.

[0026] This invention achieves a reversible dynamic covalent crosslinking network between carboxyl- or maleic anhydride-modified polyethylene and epoxy compounds in situ during melt blending under the catalysis of zinc acetate. This network significantly restricts the movement of polyethylene matrix molecular chains, greatly improving the high-temperature resistance of the film and inhibiting its recrystallization behavior during high-temperature cooking. This ensures that the film remains non-sticky, non-deformed, and non-whitening after cooking at 121°C for 30 minutes. Furthermore, the reversible exchange characteristics of the dynamic covalent bonds endow the film with thermoplasticity at high temperatures and enhance its heat-sealing strength, overcoming the heat-sealing failure and decreased transparency problems caused by traditional irradiation crosslinking or rigid filler modification. In addition, this invention only requires conventional processes of melt blending and blow molding, enabling large-scale industrial production while balancing high-temperature resistance, heat-sealing performance, transparency, and economy.

[0027] The following examples illustrate the method according to the present invention, but the invention is not limited thereto.

[0028] Example 1

[0029] Raw material formulation: High-density polyethylene (HDPE, density 0.960 g / cm³) 3 50 parts of linear low-density polyethylene (LLDPE, density 0.935 g / cm³) with a melt index of 1.5 g / 10 min. 3 25 parts of a mixture with a melt index of 1.5 g / 10 min, 25 parts of maleic anhydride-grafted low-density polyethylene (graft content 1.0%), 1.5 parts of epoxidized soybean oil, 0.5 parts of zinc acetate, 1 part of silica microparticles (opening agent), and 1 part of erucamide (slip agent).

[0030] Preparation process:

[0031] (1) Premix: Mix each component in a high-speed mixer for 8 minutes.

[0032] (2) Melt extrusion granulation: Twin screw extruder, temperature of each zone set to 150-210℃, 40rpm, water bath cooling.

[0033] (3) Blow molding film: temperature 170℃-210℃, blow ratio 2.0, traction speed 25m / min, film thickness 60μm.

[0034] Example 2

[0035] Raw material formulation: High-density polyethylene (HDPE, density 0.965 g / cm³) 3 40 parts of linear low-density polyethylene (LLDPE, density 0.940 g / cm³) with a melt index of 1.0 g / 10 min. 3 30 parts of a mixture with a melt index of 1.0 g / 10 min, 30 parts of maleic anhydride-grafted low-density polyethylene (graft content 0.8%), 1.5 parts of epoxidized soybean oil, 0.8 parts by weight of zinc acetate, 1 part of silica microparticles (opening agent), and 1 part of erucamide (slip agent).

[0036] Preparation process:

[0037] (1) Premix: Mix each component in a high-speed mixer for 10 minutes.

[0038] (2) Melt extrusion granulation: Twin screw extruder, temperature of each zone set to 150-210℃, 40rpm, water bath cooling.

[0039] (3) Blow molding film: temperature 180℃-220℃, blow ratio 1.5, traction speed 20m / min, film thickness 80μm.

[0040] Example 3

[0041] Raw material formulation: High-density polyethylene (HDPE, density 0.960 g / cm³) 340 parts of linear low-density polyethylene (LLDPE, density 0.940 g / cm³) with a melt index of 1.0 g / 10 min. 3 20 parts of melt index 1.0 g / 10 min, 40 parts of maleic anhydride-grafted low-density polyethylene (graft content 1.2%), 2 parts of epoxidized soybean oil, 1 part of zinc acetate, 1 part of silica microparticles (opening agent), and 1 part of erucamide (slip agent).

[0042] Preparation process:

[0043] (1) Premix: Mix each component in a high-speed mixer for 10 minutes.

[0044] (2) Melt extrusion granulation: Twin screw extruder, temperature of each zone set to 150-210℃, 40rpm, water bath cooling.

[0045] (3) Blow molding film: temperature 180℃-220℃, blow ratio 2, traction speed 20m / min, film thickness 70μm.

[0046] Example 4

[0047] Raw material formulation: High-density polyethylene (HDPE, density 0.965 g / cm³) 3 60 parts of linear low-density polyethylene (LLDPE, density 0.925 g / cm³) with a melt index of 1.0 g / 10 min. 3 20 parts of melt index 1.0 g / 10 min, 20 parts of ethylene-acrylic acid copolymer (acrylic acid content 6 wt%), 1 part of epoxidized soybean oil, 1 part of glycerol triglycidyl ether, 1 part of zinc acetate, 1 part of silica microparticles (opening agent), and 1 part of erucamide (slip agent).

[0048] Preparation process:

[0049] (1) Premix: Mix each component in a high-speed mixer for 5 minutes.

[0050] (2) Melt extrusion granulation: Twin screw extruder, temperature of each zone set to 150-210℃, 50rpm, water bath cooling.

[0051] (3) Blow molding film: temperature 170℃-220℃, blow ratio 2, traction speed 25m / min, film thickness 70μm.

[0052] Example 5

[0053] Raw material formulation: High-density polyethylene (HDPE, density 0.955 g / cm³) 3 40 parts of linear low-density polyethylene (LLDPE, density 0.940 g / cm³) with a melt index of 2.0 g / 10 min. 340 parts of ethylene-methacrylic acid copolymer (melt index 2.0 g / 10 min) 20 parts of bisphenol A glycidyl ether (methacrylic acid content 3 wt%) 1 part of zinc acetate 0.5 parts of silica microparticles (opening agent) 1 part of erucamide (slip agent) 1 part of ethylene-methacrylic acid copolymer (methacrylic acid content 3 wt%) 1 part of bisphenol A glycidyl ether ...

[0054] Preparation process:

[0055] (1) Premix: Mix each component in a high-speed mixer for 5 minutes.

[0056] (2) Melt extrusion granulation: Twin screw extruder, temperature of each zone set to 150-200℃, 40rpm, water bath cooling.

[0057] (3) Blow molding film: temperature 170℃-210℃, blow ratio 3, traction speed 30m / min, film thickness 50μm.

[0058] Example 6

[0059] Raw material formulation: High-density polyethylene (HDPE, density 0.960 g / cm³) 3 50 parts of linear low-density polyethylene (LLDPE, density 0.935 g / cm³) with a melt index of 1.5 g / 10 min. 3 25 parts of melt index 1.5 g / 10 min, 25 parts of ethylene-methacrylic acid copolymer (methacrylic acid content 4.0 wt%), 1.5 parts of glycerol triglycidyl ether, 0.8 parts of zinc acetate, 1 part of silica microparticles (opening agent), and 1 part of erucamide (slip agent).

[0060] Preparation process:

[0061] (1) Premix: Mix each component in a high-speed mixer for 5 minutes.

[0062] (2) Melt extrusion granulation: Twin screw extruder, temperature of each zone set to 150-210℃, 40rpm, water bath cooling.

[0063] (3) Blow molding film: temperature 170℃-210℃, blow ratio 2.0, traction speed 25m / min, film thickness 60μm.

[0064] Comparative Example 1

[0065] Raw material formulation: High-density polyethylene (HDPE, density 0.960 g / cm³) 3 50 parts by weight of linear low-density polyethylene (LLDPE, density 0.935 g / cm³) with a melt index of 1.5 g / 10 min. 325 parts by weight of melt index 1.5 g / 10 min, 25 parts by weight of maleic anhydride grafted low-density polyethylene (grafting content 1.0%), 1 part by weight of silica microparticles (opening agent), and 1 part by weight of erucamide (slip agent).

[0066] Preparation process:

[0067] (1) Premix: Mix each component in a high-speed mixer for 8 minutes.

[0068] (2) Melt extrusion granulation: Twin screw extruder, temperature of each zone set to 150-210℃, 40rpm, water bath cooling.

[0069] (3) Blow molding film: temperature 170℃-210℃, blow ratio 2.0, traction speed 25m / min, film thickness 60μm.

[0070] The membrane materials produced by the above method were subjected to performance tests, and the results are shown in the table below:

[0071]

[0072] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A retortable high-performance polyethylene film, characterized in that, It is prepared from raw materials comprising the following parts by weight: 40-60 parts of high-density polyethylene, 20-40 parts of linear low-density polyethylene, 20-40 parts of carboxyl / maleic anhydride modified polyethylene, 0.5-2 parts of epoxy compound, 0.5-1 part of zinc acetate, 1 part of opening agent, and 1 part of slip agent; wherein, the epoxy compound and the active groups in the carboxyl or maleic anhydride modified polyethylene form a reversible dynamic covalent cross-linked network under the catalysis of zinc acetate; The carboxyl-modified polyethylene is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer, wherein the content of acrylic acid or methacrylic acid is 3 wt%-6 wt%; the maleic anhydride-modified polyethylene is maleic anhydride-grafted low-density polyethylene, wherein the maleic anhydride grafting content is 0.8%-1.2%. The epoxy compounds are selected from one or more mixtures of epoxidized soybean oil, pentaerythritol glycidyl ether, glycerol triglycidyl ether, butylene glycol diglycidyl ether, and bisphenol A glycidyl ether.

2. The retortable high-performance polyethylene film according to claim 1, characterized in that: The high-density polyethylene has a density of 0.955-0.965 g / cm³ and a melt index of 1-2 g / 10 min; the linear low-density polyethylene has a density of 0.925-0.940 g / cm³ and a melt index of 1-2 g / 10 min.

3. The retortable high-performance polyethylene film according to claim 1, characterized in that: The opening agent is silica microparticles, and the slip agent is a fatty acid amide compound.

4. The retortable high-performance polyethylene film according to claim 1, characterized in that: The polyethylene film is a single-layer blown film with a thickness of 50-80μm.

5. A method for preparing a retortable high-functionality polyethylene film according to any one of claims 1-4, characterized in that, Includes the following steps: (a) Premixing: Mix the ingredients by weight in a high-speed mixer for 5-10 minutes; (b) Melt extrusion: Granulation is carried out using a twin-screw extruder at 150-210℃ and cooled by cooling water; (c) Blown film forming: The granules obtained in step (b) are melt-extruded at 170-220 ℃ using a blown film extruder, with a blow-up ratio of 1.5-3 and a traction speed of 20-30 m / min to form a film.

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