Cooking-grade high-function polyethylene film and preparation method thereof

Abstract

The invention discloses a cooking-grade high-function polyethylene film and a preparation method thereof, and belongs to the technical field of plastic films. 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 or maleic anhydride modified polyethylene, 0.5-2 parts of an epoxy compound, 0.5-1 part of zinc acetate, 1 part of an anti-blocking agent and 1 part of a slipping agent. Wherein the epoxy compound and carboxyl / anhydride group in the modified polyethylene form a dynamic covalent cross-linked network under the catalysis of zinc acetate, so that the high-temperature movement of a polyethylene molecular chain is effectively limited, and the recrystallization behavior in the cooking process is inhibited. The preparation method comprises the following steps: premixing the raw materials, melting and granulating by a double-screw extruder, and blowing and molding. The thickness of a single-layer film is 50-80 microns, the initial haze is smaller than 20%, the hot shrinkage rate is smaller than or equal to 2% after the film is cooked at 121 DEG C / 30 min, the haze change is smaller than or equal to 2%, the phenomena of whitening and stickiness do not exist, the problem that the performance of a traditional PE film is degraded after high-temperature cooking is solved, and meanwhile the excellent heat sealing performance and transparency are kept.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic films, in particular to a cooking-grade high-function polyethylene film and a preparation method thereof. Background Art

[0002] Polyethylene (PE) film is widely used in the field of food packaging due to its excellent processability, non-toxicity, chemical stability and low cost, especially in heat-sealable packaging such as jelly, meat products, and convenience foods. However, as the requirements for safety and shelf life of food packaging continue to increase, many products need to undergo high-temperature steaming and sterilization treatment above 121°C to achieve commercial sterility and extend shelf life, which places higher demands on the heat resistance of the packaging film. Due to its low melting point, ordinary PE film is prone to melting and recrystallization during high-temperature steaming, resulting in adhesion, deformation and whitening of the film material, and even heat seal failure, broken packages and air leakage, which seriously affect the sealing and food safety of the packaging. Therefore, ordinary PE film is difficult to meet the needs of long-term high-temperature sterilization, and it is urgent to improve its high-temperature resistance through modification or structural design to meet the technical requirements of modern food packaging for high-temperature stability, safety and reliability.

[0003] In order to improve the heat resistance of polyethylene films, the existing technology usually adopts a composite multilayer structure or a rigid filler modification method. For example, patent 202110521200.1 discloses a high-temperature cooking 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, and the process is complicated. Another patent 202310012356.6 proposes adding cage-type polysilsesquioxane (POSS), ethylene-vinyl alcohol copolymer (EVOH) and radiation cross-linking sensitizer to PE cooking film to enhance the rigidity of the film material and improve heat resistance.

[0004] However, rigid fillers and radiation cross-linking can reduce the heat-sealing properties of the film, and rigid fillers are difficult to disperse evenly, which can increase the haze of the film. Furthermore, radiation cross-linking requires additional equipment and post-processing, which is costly. Summary of the Invention

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

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a cooking-grade high-functional polyethylene film, 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 compounds, 0.5-1 parts of zinc acetate, 1 part of anti-blocking agent, and 1 part of lubricant; wherein the epoxy compounds and the active groups in the carboxyl or maleic anhydride modified polyethylene form a reversible dynamic covalent cross-linking network under the catalysis of zinc acetate.

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

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

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

[0010] As a preferred technical solution of the present invention, the opening agent is silicon dioxide particles, and the lubricating agent is a fatty acid amide compound.

[0011] As a preferred technical solution 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 cooking-grade high-functional polyethylene film comprises the following steps:

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

[0014] (b) Melt extrusion: using a twin-screw extruder at 150-210°C to granulate, and cooling with cooling water;

[0015] (c) Film blowing: The pellets obtained in step (2) are melt-extruded through a film blowing machine at 170-220° C., with a blow-up ratio of 1.5-3 and a pulling speed of 20-30 m / 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, the present invention forms a reversible dynamic covalent cross-linked network in situ between carboxyl or maleic anhydride modified polyethylene and epoxy compounds under the catalysis of zinc acetate. On the one hand, the network significantly restricts the movement of the polyethylene matrix molecular chain, greatly improves the high temperature resistance of the film material and inhibits its recrystallization behavior during high-temperature cooking, so that the film remains non-sticky, non-deformed, and non-whitening after being cooked at 121°C for 30 minutes; on the other hand, the reversible exchange characteristics of the dynamic covalent bond enable the film to remain thermoplastic in a high temperature environment and enhance the heat sealing strength, overcoming the problems of heat sealing failure and decreased transparency caused by traditional radiation cross-linking or rigid filler modification; in addition, the present invention only requires the conventional processes of melt blending and blow molding, and can realize industrial large-scale production, taking into account high temperature resistance, heat sealing performance, transparency and economy. DETAILED DESCRIPTION

[0017] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0018] The invention discloses a cooking-grade high-function polyethylene film and a preparation method thereof.

[0019] The polyethylene film 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 compounds, 0.5-1 parts of zinc acetate, 1 part of an anti-blocking agent, and 1 part of a lubricant; wherein the epoxy compounds and the active groups in the carboxyl or maleic anhydride modified polyethylene form a reversible dynamic covalent cross-linking network under the catalysis of zinc acetate.

[0020] Epoxy compounds undergo dynamic covalent cross-linking with carboxyl or maleic anhydride groups in modified polyethylene to form a reversible ester bond network structure, which effectively restricts the movement of polyethylene molecular chains at high temperatures, significantly improves the film's high-temperature resistance, and inhibits recrystallization behavior during high-temperature cooking, thereby overcoming the defects of traditional polyethylene films such as whitening and inner layer adhesion after cooking. The single-layer film of the present invention has a thickness of 50-80μm, an initial haze of <20%, a heat shrinkage rate of ≤2% and a haze change of ≤2% after cooking at 121℃ / 30min, without 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, and is suitable for high-temperature sterilization packaging of food.

[0021] In this embodiment, the opening agent is silicon dioxide particles; the lubricant is a fatty acid amide compound; the epoxy compound is selected from one or more mixtures of epoxy soybean oil, pentaerythritol glycidyl ether, glycerol triglycidyl ether, butanediol diglycidyl ether, and bisphenol A glycidyl ether; the density of the high-density polyethylene is 0.955-0.965g / cm3, and the melt index is 1-2g / 10min; the density of the linear low-density polyethylene is 0.925-0.940g / cm 3 , a melt index of 1-2 g / 10 min; the carboxyl-modified polyethylene is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer, wherein the acrylic acid or methacrylic acid content is 3wt%-6wt%; the maleic anhydride-modified polyethylene is a maleic anhydride-grafted low-density polyethylene, and the maleic anhydride grafted 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 cooking-grade high-functional polyethylene film comprises the following steps:

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

[0024] (b) Melt extrusion: using a twin-screw extruder at 150-210°C to granulate, and cooling with cooling water;

[0025] (c) Film blowing: The pellets obtained in step (2) are melt-extruded through a film blowing machine at 170-220° C., with a blow-up ratio of 1.5-3 and a pulling speed of 20-30 m / min to form a film.

[0026] The present invention forms a reversible dynamic covalent cross-linked network in situ between carboxyl or maleic anhydride-modified polyethylene and an epoxy compound under the catalysis of zinc acetate during the melt blending process. On the one hand, this network significantly restricts the movement of the polyethylene matrix molecular chains, greatly improving the high-temperature resistance of the film material and inhibiting its recrystallization behavior during high-temperature cooking, so that the film remains non-sticky, non-deformed, and non-whitening after being cooked at 121°C for 30 minutes; on the other hand, the reversible exchange characteristics of the dynamic covalent bonds enable the film to maintain thermoplasticity in a high-temperature environment and enhance the heat-sealing strength, overcoming the problems of heat-sealing failure and decreased transparency caused by traditional radiation cross-linking or rigid filler modification; in addition, the present invention only requires conventional processes of melt blending and blow molding, and can achieve industrial large-scale production, taking into account high-temperature resistance, heat-sealing performance, transparency and economy.

[0027] The method according to the present invention is described below by way of examples, but the present invention is not limited thereto.

[0028] Example 1

[0029] Raw material formula: high-density polyethylene (HDPE, density 0.960g / cm 3 , melt index 1.5g / 10min) 50 parts, linear low density polyethylene (LLDPE, density 0.935g / cm 3 , melt index 1.5g / 10min) 25 parts, maleic anhydride grafted low-density polyethylene (grafting content 1.0%) 25 parts, epoxidized soybean oil 1.5 parts, zinc acetate 0.5 parts, silicon dioxide particles (opening agent) 1 part, erucamide (slipping agent) 1 part.

[0030] Preparation process:

[0031] (1) Premixing: Mix all components in a high-speed mixer for 8 minutes.

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

[0033] (3) Film blowing: temperature 170℃-210℃, blow-up ratio 2.0, pulling speed 25m / min, film thickness 60μm.

[0034] Example 2

[0035] Raw material formula: high-density polyethylene (HDPE, density 0.965g / cm 3 , melt index 1.0g / 10min) 40 parts, linear low density polyethylene (LLDPE, density 0.940g / cm 3 , melt index 1.0g / 10min) 30 parts, maleic anhydride grafted low-density polyethylene (grafting content 0.8%) 30 parts, epoxidized soybean oil 1.5 parts, zinc acetate 0.8 weight parts, silica particles (opening agent) 1 part, erucamide (slip agent) 1 part.

[0036] Preparation process:

[0037] (1) Premixing: Mix all components in a high-speed mixer for 10 minutes.

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

[0039] (3) Film blowing: temperature 180℃-220℃, blow-up ratio 1.5, pulling speed 20m / min, film thickness 80μm.

[0040] Example 3

[0041] Raw material formula: high-density polyethylene (HDPE, density 0.960g / cm 3, melt index 1.0g / 10min) 40 parts, linear low density polyethylene (LLDPE, density 0.940g / cm 3 , melt index 1.0g / 10min) 20 parts, maleic anhydride grafted low-density polyethylene (grafting content 1.2%) 40 parts, epoxidized soybean oil 2 parts, zinc acetate 1 part, silicon dioxide particles (opening agent) 1 part, erucamide (slip agent) 1 part.

[0042] Preparation process:

[0043] (1) Premixing: Mix all components in a high-speed mixer for 10 minutes.

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

[0045] (3) Film blowing: temperature 180℃-220℃, blow-up ratio 2, pulling speed 20m / min, film thickness 70μm.

[0046] Example 4

[0047] Raw material formula: high-density polyethylene (HDPE, density 0.965g / cm 3 , melt index 1.0g / 10min) 60 parts, linear low density polyethylene (LLDPE, density 0.925g / cm 3 , melt index 1.0g / 10min) 20 parts, ethylene-acrylic acid copolymer (acrylic acid content 6wt%) 20 parts, epoxidized soybean oil 1 part, glycerol triglycidyl ether 1 part, zinc acetate 1 part, silica particles (opening agent) 1 part, erucamide (slipping agent) 1 part.

[0048] Preparation process:

[0049] (1) Premixing: Mix all components in a high-speed mixer for 5 minutes.

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

[0051] (3) Film blowing: temperature 170℃-220℃, blow-up ratio 2, pulling speed 25m / min, film thickness 70μm.

[0052] Example 5

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

[0054] Preparation process:

[0055] (1) Premixing: Mix all components in a high-speed mixer for 5 minutes.

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

[0057] (3) Film blowing: temperature 170℃-210℃, blow-up ratio 3, pulling speed 30m / min, film thickness 50μm.

[0058] Example 6

[0059] Raw material formula: high-density polyethylene (HDPE, density 0.960g / cm 3 , melt index 1.5g / 10min) 50 parts, linear low density polyethylene (LLDPE, density 0.935g / cm 3 , melt index 1.5g / 10min) 25 parts, ethylene-methacrylic acid copolymer (methacrylic acid content is 4.0wt%) 25 parts, glycerol triglycidyl ether 1.5 parts, zinc acetate 0.8 parts, silica particles (opening agent) 1 part, erucamide (slip agent) 1 part.

[0060] Preparation process:

[0061] (1) Premixing: Mix all components in a high-speed mixer for 5 minutes.

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

[0063] (3) Film blowing: temperature 170℃-210℃, blow-up ratio 2.0, pulling speed 25m / min, film thickness 60μm.

[0064] Comparative Example 1

[0065] Raw material formula: high-density polyethylene (HDPE, density 0.960g / cm 3 , melt index 1.5g / 10min) 50 parts by weight, linear low-density polyethylene (LLDPE, density 0.935g / cm 3, melt index 1.5g / 10min) 25 weight parts, maleic anhydride grafted low-density polyethylene (grafting content 1.0%) 25 weight parts, silica particles (opening agent) 1 weight part, erucamide (slip agent) 1 weight part.

[0066] Preparation process:

[0067] (1) Premixing: Mix all components in a high-speed mixer for 8 minutes.

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

[0069] (3) Film blowing: temperature 170℃-210℃, blow-up ratio 2.0, pulling speed 25m / min, film thickness 60μm.

[0070] The performance test of the membrane material produced by the above method is shown in the following table:

[0071]

[0072] The above shows and describes 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 above embodiments and descriptions are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A cooking grade high-function polyethylene film, characterized in that: The invention 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 compounds, 0.5-1 parts of zinc acetate, 1 part of anti-blocking agent, and 1 part of lubricant; wherein the epoxy compounds and the active groups in the carboxyl or maleic anhydride modified polyethylene form a reversible dynamic covalent cross-linking network under the catalysis of zinc acetate.

2. The cooking-grade high-functional polyethylene film according to claim 1, characterized in that: The density of the high-density polyethylene is 0.955-0.965 g / cm 3 , melt index 1-2g / 10min; the density of the linear low-density polyethylene is 0.925-0.940g / cm 3 , the melt index is 1-2g / 10min.

3. The cooking-grade high-functional polyethylene film according to claim 1, characterized in that: The carboxyl modified polyethylene is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer, wherein the acrylic acid or methacrylic acid content is 3wt%-6wt%; the maleic anhydride modified polyethylene is a maleic anhydride grafted low-density polyethylene, and the maleic anhydride grafted content is 0.8%-1.2%.

4. The cooking-grade high-functional polyethylene film according to claim 1, characterized in that: The epoxy compound is selected from one or more mixtures of epoxy soybean oil, pentaerythritol glycidyl ether, glycerol triglycidyl ether, butanediol diglycidyl ether, and bisphenol A glycidyl ether.

5. The cooking-grade high-functional polyethylene film according to claim 1, characterized in that: The opening agent is silicon dioxide particles, and the lubricant is a fatty acid amide compound.

6. The cooking-grade high-functional polyethylene film according to claim 1, characterized in that: The polyethylene film is a single-layer blown film with a thickness of 50-80 μm.

7. A method for preparing a cooking-grade high-functional polyethylene film according to any one of claims 1 to 6, characterized in that: The following steps are involved: (a) Premixing: Mix the raw materials by weight in a high-speed mixer for 5-10 minutes; (b) Melt extrusion: using a twin-screw extruder at 150-210°C to granulate, and cooling with cooling water; (c) Film blowing: The pellets obtained in step (2) are melt-extruded through a film blowing machine at 170-220° C., with a blow-up ratio of 1.5-3 and a pulling speed of 20-30 m / min to form a film.

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