A fully polyethylene composite film and its preparation method

Abstract

This application relates to the field of food packaging materials, and specifically discloses a fully polyethylene composite film and a preparation method thereof. The fully polyethylene composite film includes a surface layer, an intermediate layer, and a base layer. The surface layer includes high-density polyethylene and an antioxidant; the intermediate layer includes low-density polyethylene, a quaternary ammonium salt antibacterial agent, and silicone; the base layer includes high-molecular-weight polyethylene; the intermediate layer is treated by electron beam irradiation; the preparation method is as follows: after mixing high-density polyethylene and an antioxidant, the surface layer is prepared by melt blending; the quaternary ammonium salt antibacterial agent and silicone are mixed with low-density polyethylene, and after melt blending, the intermediate layer is treated by electron beam irradiation; high-molecular-weight polyethylene is prepared into the base layer by melt blending; and the composite film is obtained by hot pressing. It has the advantages of ensuring good barrier and antibacterial properties of the packaging film while effectively improving the stability of the film.

Description

Technical Field

[0001] This application relates to the technical field of food packaging materials, and more specifically, it relates to a fully polyethylene composite film and a preparation method thereof. Background Art

[0002] Food packaging materials refer to the packaging containers and materials used to protect, store, and transport food. These materials usually include plastic films, papers, metal cans, and glass bottles, etc. With the enhancement of people's awareness of environmental protection and the improvement of food safety requirements, traditional packaging materials have been gradually phased out, and polyethylene has become an ideal alternative due to its advantages such as non-toxic, odorless, free of harmful substances, and easy to recycle.

[0003] Polyethylene composite film food packaging materials have excellent physical properties and chemical stability, and can effectively protect food from the influence of the external environment. At the same time, fully polyethylene materials also have excellent barrier properties and moisture resistance, and can effectively prevent food from spoiling and rotting. Therefore, fully polyethylene composite films are widely used in various food packaging fields.

[0004] Currently, as an emerging food packaging technology that can meet the changing market demands, antibacterial packaging has attracted more and more attention. This technology can effectively avoid food spoilage caused by microorganisms to ensure food safety and extend the product shelf life, and is considered a feasible method to replace the direct addition of chemical preservatives to perishable foods. Although certain research has been conducted on the preparation technology of polyethylene packaging films, there are still problems with poor stability of the packaging films while improving barrier, antibacterial and other properties. Therefore, it is necessary to provide a new technical solution to overcome the problems existing in the prior art. Summary of the Invention

[0005] In order to ensure good barrier and antibacterial properties of the packaging film while effectively improving the stability of the film, this application provides a fully polyethylene composite film and a preparation method thereof.

[0006] In the first aspect, this application provides a fully polyethylene composite film, adopting the following technical solution:

[0007] A fully polyethylene composite film, the composite film includes a surface layer, an intermediate layer, and a base layer. The raw materials of the surface layer include high-density polyethylene and an antioxidant; the raw materials of the intermediate layer include low-density polyethylene, a quaternary ammonium salt antibacterial agent, and silicone; the raw materials of the base layer include high-molecular-weight polyethylene. After the intermediate layer is treated by electron beam irradiation, the surface layer, the intermediate layer, and the base layer are compounded to obtain the composite film.

[0008] By adopting the above technical solutions, the surface layer uses high-density polyethylene, which usually has better wear resistance, thus enhancing the service life of the composite film; high-density polyethylene usually has good weather resistance, which can protect the internal structure of the composite film from the influence of the external environment and extend its service life; low-density polyethylene as the intermediate layer can increase the flexibility of the composite film, making it easier to bend and form to meet different application requirements; high-molecular-weight polyethylene as the base layer usually has higher tensile strength and modulus, which helps to improve the overall strength of the composite film; by selecting the above types of polyethylene and making reasonable combinations, the manufacturing cost can be reduced while ensuring performance.

[0009] By introducing quaternary ammonium salt antibacterial agents and silicone into the intermediate layer, antibacterial agents or antibacterial functional groups are introduced into the intermediate layer to enhance the antibacterial performance of the composite film; silicone contains oligomers with active groups, which have excellent weather resistance, water resistance and high-temperature resistance, helping to maintain the freshness and safety of the products inside the package and can also effectively improve the moisture-proof and moisture-barrier properties of the film; the quaternary ammonium salt antibacterial agent can form a dense antibacterial film on the surface of the silicone, preventing the invasion and reproduction of microorganisms. At the same time, the organic groups in the silicone material form hydrogen bonds, van der Waals forces and other interactions with the quaternary ammonium salt, enhancing the stability and persistence of the quaternary ammonium salt antibacterial agent on the material surface; in addition, the microporous structure in the silicone material also provides more adsorption sites for the quaternary ammonium salt antibacterial agent, further improving the antibacterial effect.

[0010] Through electron beam radiation treatment, the high-energy electron beam radiation energy causes cross-linking and curing of the coating polymer, improving the surface polarity, increasing the surface roughness or introducing new functional groups, thus improving adhesion, etc. A dense and stable film with good weather resistance can be formed on the surface of the intermediate layer, effectively blocking the penetration of substances such as water vapor and oxygen, thereby enhancing the barrier performance of the composite film; it can also effectively resist the erosion of factors such as ultraviolet rays and oxidation, thus extending the service life of the composite film; and through the electron beam radiation technology, chemical reactions can occur on the material surface to form a strong adhesive layer, improving the surface performance and adhesion performance of the intermediate layer; when the intermediate layer is irradiated by the electron beam, due to the generation of free radicals, oxidation reactions will occur inside the film, and with the action of silicone, this oxidation reaction can be inhibited to a certain extent, thereby improving the antioxidant performance of the intermediate layer and also improving the oxygen barrier performance of the film. Electron beam radiation can also promote the compatibility of the quaternary ammonium salt antibacterial agent with low-density polyethylene, which can increase the dispersibility and permeability of the antibacterial agent in the material, making it more effectively penetrate to the surface and inside of the material, thus playing a more comprehensive antibacterial role, and can also change the molecular structure of the antibacterial agent to make it more antibacterial active and stable.

[0011] Preferably, the raw materials of the intermediate layer include: 80-100 parts of low-density polyethylene, 0.1-0.2 parts of quaternary ammonium salt antibacterial agent, and 2-8 parts of silicone.

[0012] By adopting the above technical solution and preparing the intermediate layer with the above raw material ratio, the weather resistance and antibacterial property of the film can be further improved, and at the same time, the stability performance of the film can be further enhanced.

[0013] Preferably, the thickness of the surface layer is 16-20 μm, the thickness of the intermediate layer is 28-32 μm, and the thickness of the base layer is 38-42 μm.

[0014] By adopting the above technical solution and the above interlayer thickness structure, the composite film has the advantages of good waterproof, moisture-proof, gas barrier, mechanical strength, processing performance, etc., can effectively protect the items in the package from external damage, can be subjected to processing treatments such as heat sealing, embossing, printing, etc., is convenient for packaging and labeling, can effectively prevent the penetration of gases such as oxygen and carbon dioxide, and maintain the freshness and nutritional value of the items in the package.

[0015] Preferably, the quaternary ammonium salt antibacterial agent is benzethonium chloride, didodecyldimethylammonium chloride, dodecyltrimethylammonium chloride or benzalkonium bromide.

[0016] By adopting the above technical solution, the above quaternary ammonium salt antibacterial agents all have good antibacterial properties, and there are certain van der Waals forces, hydrogen bonds and other interactions between them and the microporous structure on the surface of the silicone material, so that the quaternary ammonium salt antibacterial agent can be attached to the surface of the silicone material by physical adsorption; the active groups in the quaternary ammonium salt antibacterial agent can react chemically with functional groups such as hydroxyl groups and amino groups on the surface of the silicone material to form chemical bonds, so as to form a firm chemical bond between the quaternary ammonium salt antibacterial agent and the silicone material; the above quaternary ammonium salt antibacterial agents can enhance the antibacterial property of the silicone material, making it have a stronger killing effect on microorganisms such as bacteria and molds; second, the silicone material can improve the stability and persistence of the above quaternary ammonium salt antibacterial agent, making it not easy to be decomposed and lost on the material surface.

[0017] Preferably, when the intermediate layer is treated by electron beam radiation, the temperature is 50-80 °C, the pressure is 100-300 kPa, the radiation dose is 5-8 kGy, and the treatment time is 10-15 min.

[0018] By adopting the above technical solution, electron beam radiation treatment with the above parameters can effectively kill bacteria and microorganisms on the film surface, improve its barrier performance, mechanical properties, thermal stability, etc., increase the surface tension of the all-polyethylene film, make it less likely to be penetrated by water molecules, and also improve the adhesion between the all-polyethylene film and other materials, making it easier to bond and seal. These effects contribute to improving the safety, quality, and service life of food packaging.

[0019] Preferably, the melt index of the low-density polyethylene is 0.5 - 1.3 g / 10 min, and the density is 0.915 - 0.925 g / cm 3 ; the melt index of the high-density polyethylene is 1.2 - 1.5 g / 10 min, and the density is 0.942 - 0.956 g / cm 3 ; the melt index of the high-molecular-weight polyethylene is 0.1 - 0.4 g / 10 min, and the density is 0.932 - 0.948 g / cm 3 .

[0020] By adopting the above technical solution, each layer with the melt index and density within the above ranges can provide better processing performance. When making food packaging films, it can be more easily fused and formed, thus improving production efficiency; it can also provide better mechanical properties, and the prepared food packaging films will be tougher and more durable, and can better withstand friction and pressure in daily use. It can better control the surface roughness of the material and reduce the attachment and growth of microorganisms, which makes the prepared food packaging films have better hygienic properties and helps maintain food safety.

[0021] Preferably, the antioxidant is a hindered phenol antioxidant.

[0022] Preferably, the hindered phenol antioxidant is 2,6-tert-butyl-4-methylphenol or bis(2-thienyl) disulfide.

[0023] By adopting the above technical solution, the compound use of the hindered phenol antioxidant and silicone can produce good synergistic effects. The hindered phenol antioxidant mainly inhibits the oxidation reaction of the material by capturing free radicals or peroxides, while silicone can form a protective layer to prevent moisture and oxygen from entering the material interior, thus effectively extending the storage and service life of the material. When the two are compounded and used, they can complement each other and enhance the antioxidant effect; both the hindered phenol antioxidant and silicone have good thermal stability and can improve the heat resistance of the material. When the two are compounded and used, they can further enhance the thermal stability of the material and keep it in good performance under high-temperature environments.

[0024] Preferably, the silicone is methyltrimethylsiloxysilane, vinyltrimethoxysilane, γ-glycidyltrimethoxysilane, 3-aminopropyltriethoxysilane or aminomethyltrimethylsilane.

[0025] Preferably, the silicone is 3-aminopropyltriethoxysilane or aminomethyltrimethylsilane.

[0026] By adopting the above technical scheme, the above silicone material is used to introduce amino functional groups, so that it has better dispersibility, polarity, reactivity, etc. with polyethylene materials, and the synergistic effect with quaternary ammonium salt antibacterial agents is improved; after the amino functional groups are introduced into the silicone, they can interact with the hydroxyl functional groups in the hindered phenol antioxidant to form hydrogen bonds, thereby enhancing the synergistic effect between the silicone and the hindered phenol antioxidant, promoting the dispersion and combination of the silicone and the hindered phenol antioxidant in the material, and improving the antioxidant performance and thermal stability of the material.

[0027] In a second aspect, the present application provides a method for preparing a fully polyethylene composite film, using the following technical solution:

[0028] A method for preparing a full polyethylene composite film, the preparation steps are as follows:

[0029] Preparing the surface layer: mixing high-density polyethylene and an antioxidant, and preparing the surface layer by melt blending;

[0030] Preparation of the middle layer: firstly, the quaternary ammonium antibacterial agent and silicone are mixed and stirred at 60-80° C. and a stirring speed of 50-150 revolutions per minute, and then mixed with low-density polyethylene to prepare the middle layer by melt blending, and then the middle layer is subjected to electron beam radiation treatment;

[0031] Preparing a base layer: preparing a base layer by melt blending a high molecular weight polyethylene;

[0032] Composite: The surface layer, the middle layer and the base layer are stacked in sequence, and the layers are composited together by hot pressing to obtain a composite film.

[0033] By adopting the above technical scheme, the prepared composite film has a three-layer structure, the surface layer can provide good antioxidant properties, the middle layer has antibacterial and antioxidant functions, and the base layer has high strength and wear resistance. The layers are prepared by a melt blending method, which can achieve continuous production with high production efficiency. At the same time, the layers have good adhesion properties, which improves the overall stability of the composite film; electron beam radiation treatment can further enhance the antioxidant properties of the middle layer, improve its stability and durability as well as the adhesion performance with other layers; each step in the preparation process is simple to operate and easy to control, and the prepared composite film has good resistance, antibacterial and stability.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. Since the present application adopts multi-layer composite to prepare the all-polyethylene composite film, high-density polyethylene, low-density polyethylene, and high molecular weight polyethylene are used as substrates respectively, and quaternary ammonium antibacterial agents and silicone are introduced into the middle layer, the quaternary ammonium antibacterial agent can form a dense antibacterial film on the surface of silicone, preventing the invasion and reproduction of microorganisms. At the same time, the organic groups in the silicone material form hydrogen bonds, van der Waals forces and other interactions with the quaternary ammonium salt, thereby enhancing the stability and durability of the quaternary ammonium antibacterial agent on the surface of the material.

[0036] 2. In the present application, it is preferred to modify the silicone by aminomethyltrimethylsilane to introduce amino functional groups into the silicone, so that it has better dispersibility, polarity, reactivity, etc. with polyethylene materials, and improves the synergistic effect with quaternary ammonium salt antibacterial agents, and can interact with the hydroxyl functional groups in the hindered phenol antioxidant to form hydrogen bonds, thereby enhancing the synergistic effect between silicone and hindered phenol antioxidants, which can promote the dispersion and combination of silicone and hindered phenol antioxidants in the material, and improve the antioxidant properties and thermal stability of the material.

[0037] 3. The method of the present application can realize continuous production with high production efficiency by preparing each layer of the surface layer, the middle layer and the base layer through a melt blending method. At the same time, each layer has good adhesion performance, which improves the overall stability of the composite film. Each step in the preparation process is simple to operate and easy to control. The prepared composite film has good resistance, antibacterial properties and stability. DETAILED DESCRIPTION

[0038] The present application is further described in detail below with reference to the embodiments.

[0039] The sources of raw materials used in this application are as follows:

[0040] Table 1 Source of raw materials

[0041] Raw material name Purchase source High density polyethylene Shanghai Furun Plastic Technology Co., Ltd. Low density polyethylene Dongguan Guangyuan New Material Technology Co., Ltd. High molecular weight polyethylene Dongguan Yisheng Plastic Co., Ltd. Maleic anhydride grafted PE binder Dongguan Shangyi Plastic Co., Ltd. Bis(2-thienyl) disulfide Hubei Langbowan Biomedicine Co., Ltd.

[0042] Example

[0043] Example 1

[0044] A full polyethylene composite film, comprising a surface layer, an intermediate layer and a base layer;

[0045] The surface layer includes 45 kg of high-density polyethylene and 0.225 kg of antioxidant. The melt index of high-density polyethylene is 1.2-1.5 g / 10 min and the density is 0.942-0.956 g / cm 3 , the antioxidant is 2,2'-ethylenebis[3-tert-butyl-4-methylphenol.

[0046] The intermediate layer includes 80 kg of low-density polyethylene, 0.2 kg of quaternary ammonium salt antibacterial agent, and 2 kg of silicone. The melt index of the low-density polyethylene is 0.5 - 1.3 g / 10 min, and the density is 0.915 - 0.925 g / cm 3 . The quaternary ammonium salt antibacterial agent is benzethonium chloride, and the silicone is dodecyl silanoxy silicone oil.

[0047] The base layer includes 90 kg of high molecular weight polyethylene. The melt index of the high molecular weight polyethylene is 0.1 - 0.4 g / 10 min, and the density is 0.932 - 0.948 g / cm 3 .

[0048] The preparation steps of the all-polyethylene composite film are as follows:

[0049] Prepare the surface layer: After mixing high-density polyethylene and antioxidant in the above proportions, perform melt blending at 160 °C, and finally extrude into a film material through an extruder at 180 °C. When extruding, the screw speed is 25 rpm, and the traction speed is 15 m / min; then adjust the traction speed for stretching treatment at 150 °C, and perform heat setting at 95 °C. Finally, cool under the conditions of a cooling temperature between 30 °C and a wind speed of 1.5 m / s to obtain a surface layer with a thickness of 23 ± 2 μm;

[0050] Prepare the intermediate layer: First, mix and stir the quaternary ammonium salt antibacterial agent and silicone at 60 °C and a stirring speed of 50 revolutions per minute, then mix with the low-density polyethylene in the above proportions, perform melt blending at 150 °C, and finally extrude into a film material through an extruder at 180 °C. When extruding, the screw speed is 25 rpm, and the traction speed is 15 m / min; then adjust the traction speed for stretching treatment at 120 °C, and perform heat setting at 95 °C; then perform electron beam radiation treatment at a temperature of 50 °C, a pressure of 100 kPa, a radiation dose of 5 kGy, and a treatment time of 15 min in a nitrogen environment. Finally, cool under the conditions of a cooling temperature between 30 °C and a wind speed of 1.5 m / s to obtain an intermediate layer with a thickness of 25 ± 2 μm;

[0051] Prepare the base layer: Perform melt blending of the high molecular weight polyethylene at 150 °C, and finally extrude into a film material through an extruder at 180 °C. When extruding, the screw speed is 25 rpm, and the traction speed is 15 m / min; then adjust the traction speed for stretching treatment at 120 °C, and perform heat setting at 95 °C. Finally, cool under the conditions of a cooling temperature between 30 °C and a wind speed of 1.5 m / s to obtain a base layer with a thickness of 40 ± 2 μm;

[0052] Composite: After coating maleic anhydride grafted PE adhesive on both sides of the middle layer, the surface layer, the middle layer and the base layer are stacked and bonded in sequence, and then hot-pressed at a temperature of 180° C. and a pressure of 20 bar to obtain a composite film.

[0053] Example 2

[0054] A full polyethylene composite film, comprising a surface layer, an intermediate layer and a base layer;

[0055] The surface layer includes 50 kg of high-density polyethylene and 0.150 kg of antioxidant. The melt index of high-density polyethylene is 1.2-1.5 g / 10 min and the density is 0.942-0.956 g / cm 3 , the antioxidant is 2,2'-ethylenebis[3-tert-butyl-4-methylphenol.

[0056] The middle layer includes 100 kg of low-density polyethylene, 0.1 kg of quaternary ammonium salt antibacterial agent and 8 kg of silicone. The melt index of low-density polyethylene is 0.5-1.3 g / 10 min and the density is 0.915-0.925 g / cm 3 The quaternary ammonium antibacterial agent is benzyl ethylamine chloride, and the silicone uses n-dodecylsiloxy silicone oil.

[0057] The base layer includes 90 kg of high molecular weight polyethylene, the melt index of the high molecular weight polyethylene is 0.1-0.4 g / 10 min, and the density is 0.932-0.948 g / cm 3 .

[0058] The steps for preparing the all-polyethylene composite film are as follows:

[0059] Preparation of the surface layer: After mixing high-density polyethylene and antioxidant in the above proportion, melt blending is performed at 160°C, and finally extruding into a film material through an extruder at 180°C, the screw speed is 25rpm, and the pulling speed is 15m / min during extrusion; then adjusting the pulling speed at a temperature of 150°C for stretching treatment, and heat-preserving and shaping at a temperature of 95°C, and finally cooling at a cooling temperature of 30°C and a wind speed of 1.5m / s to obtain a surface layer with a thickness of 23±2 microns;

[0060] Preparation of the intermediate layer: First, the quaternary ammonium salt antibacterial agent and silicone are mixed and stirred at 60 °C with a stirring speed of 50 revolutions per minute, and then mixed with low-density polyethylene in the above ratio. Melting and blending are carried out at 150 °C, and finally, a film material is extruded through an extruder at 180 °C. When extruding, the screw speed is 25 rpm and the traction speed is 15 m / min; then, the traction speed is adjusted for stretching treatment at a temperature of 120 °C, and heat setting is carried out at a temperature of 95 °C; then, the intermediate film layer is subjected to electron beam radiation treatment at a temperature of 80 °C, a pressure of 300 kPa, a radiation dose of 8 kGy, and a treatment time of 10 min under a nitrogen environment. Finally, it is cooled under the conditions of a cooling temperature between 30 °C and a wind speed of 1.5 m / s to obtain an intermediate layer with a thickness of 25 ± 2 μm;

[0061] Preparation of the base layer: High molecular weight polyethylene is melt-blended at 150 °C, and finally, a film material is extruded through an extruder at 180 °C. When extruding, the screw speed is 25 rpm and the traction speed is 15 m / min; then, the traction speed is adjusted for stretching treatment at a temperature of 120 °C, and heat setting is carried out at a temperature of 95 °C. Finally, it is cooled under the conditions of a cooling temperature between 30 °C and a wind speed of 1.5 m / s to obtain a base layer with a thickness of 40 ± 2 μm;

[0062] Lamination: After coating maleic anhydride-grafted PE binder on both sides of the intermediate layer, the surface layer, intermediate layer, and base layer are sequentially laminated and bonded, and then hot-pressed and laminated at a temperature of 180 °C and a pressure of 20 bar to obtain a composite film.

[0063] Example 3

[0064] A fully polyethylene composite film, comprising a surface layer, an intermediate layer, and a base layer;

[0065] Among them, the surface layer includes 43 kg of high-density polyethylene and 0.172 kg of antioxidant. The melt index of high-density polyethylene is 1.2 - 1.5 g / 10 min, and the density is 0.942 - 0.956 g / cm 3 , and the antioxidant is 2,2'-ethylidenebis[3-tert-butyl-4-methylphenol].

[0066] The intermediate layer includes 90 kg of low-density polyethylene, 0.15 kg of quaternary ammonium salt antibacterial agent, and 5 kg of silicone. The melt index of low-density polyethylene is 0.5 - 1.3 g / 10 min, and the density is 0.915 - 0.925 g / cm 3 , the quaternary ammonium salt antibacterial agent is benzalkonium chloride, and the silicone is n-dodecyl silane oxy silicone oil.

[0067] The base layer includes 90 kg of high molecular weight polyethylene, the melt index of the high molecular weight polyethylene is 0.1 - 0.4 g / 10 min, and the density is 0.932 - 0.948 g / cm 3 .

[0068] The preparation steps of the all - polyethylene composite film are as follows:

[0069] Prepare the surface layer: After mixing high - density polyethylene and antioxidant in the above - mentioned ratio, conduct melt blending at 160 °C, and finally extrude into a film material through an extruder at 180 °C. When extruding, the screw speed is 25 rpm and the traction speed is 15 m / min; then adjust the traction speed for stretching treatment at a temperature of 150 °C, and carry out heat setting at a temperature of 95 °C. Finally, cool under the conditions that the cooling temperature is between 30 °C and the wind speed is 1.5 m / s to obtain a surface layer with a thickness of 23 ± 2 μm;

[0070] Prepare the intermediate layer: First, mix and stir the quaternary ammonium salt antibacterial agent and silicone at 60 °C with a stirring speed of 50 revolutions per minute, then mix with low - density polyethylene in the above - mentioned ratio, conduct melt blending at 150 °C, and finally extrude into a film material through an extruder at 180 °C. When extruding, the screw speed is 25 rpm and the traction speed is 15 m / min; then adjust the traction speed for stretching treatment at a temperature of 120 °C, and carry out heat setting at a temperature of 95 °C; then conduct electron beam radiation treatment on the intermediate film layer at a temperature of 65 °C, a pressure of 200 kPa, a radiation dose of 6.5 kGy, and a treatment time of 13 min under a nitrogen environment. Finally, cool under the conditions that the cooling temperature is between 30 °C and the wind speed is 1.5 m / s to obtain an intermediate layer with a thickness of 25 ± 2 μm;

[0071] Prepare the base layer: Conduct melt blending of high molecular weight polyethylene at 150 °C, and finally extrude into a film material through an extruder at 180 °C. When extruding, the screw speed is 25 rpm and the traction speed is 15 m / min; then adjust the traction speed for stretching treatment at a temperature of 120 °C, and carry out heat setting at a temperature of 95 °C. Finally, cool under the conditions that the cooling temperature is between 30 °C and the wind speed is 1.5 m / s to obtain a base layer with a thickness of 40 ± 2 μm;

[0072] Lamination: After coating maleic anhydride - grafted PE binder on both sides of the intermediate layer, stack and bond the surface layer, intermediate layer and base layer in sequence, and then conduct hot - press lamination at a temperature of 180 °C and a pressure of 20 bar to obtain the composite film.

[0073] Example 4

[0074] A fully polyethylene composite film, which is different from that of Example 1 in that the thickness of the surface layer obtained is 18 ± 2 μm, the thickness of the intermediate layer is 30 ± 2 μm, and the thickness of the base layer is 40 ± 2 μm.

[0075] Example 5

[0076] A fully polyethylene composite film, which is different from that of Example 4 in that the quaternary ammonium salt antibacterial agent is dioctyldimethylammonium chloride.

[0077] Example 6

[0078] A fully polyethylene composite film, which is different from that of Example 4 in that the quaternary ammonium salt antibacterial agent is dodecyltrimethylammonium chloride.

[0079] Example 7

[0080] A fully polyethylene composite film, which is different from that of Example 4 in that the quaternary ammonium salt antibacterial agent is benzalkonium bromide.

[0081] Example 8

[0082] A fully polyethylene composite film, which is different from that of Example 4 in that the antioxidant is the hindered phenol antioxidant 2,6-tert-butyl-4-methylphenol.

[0083] Example 9

[0084] A fully polyethylene composite film, which is different from that of Example 4 in that the antioxidant is the hindered phenol antioxidant bis(2-thienyl) disulfide.

[0085] Example 10

[0086] A fully polyethylene composite film, which is different from that of Example 8 in that the silicone is methyltrimethoxysilane.

[0087] Example 11

[0088] A fully polyethylene composite film, which is different from that of Example 8 in that the silicone is vinyltrimethoxysilane.

[0089] Example 12

[0090] A fully polyethylene composite film, which is different from that of Example 8 in that the silicone is γ-glycidoxytrimethoxysilane.

[0091] Example 13

[0092] A fully polyethylene composite film, which is different from that of Example 8 in that the silicone is 3-aminopropyltriethoxysilane.

[0093] Example 14

[0094] A fully polyethylene composite film, which is different from that of Example 8 in that the silicone is aminomethyltrimethylsilane.

[0095] Comparative example

[0096] Comparative Example 1

[0097] A fully polyethylene composite film, which is different from that of Example 1 in that the raw materials of the intermediate layer do not include silicone.

[0098] Comparative Example 2

[0099] A fully polyethylene composite film, which is different from that of Example 1 in that the intermediate layer is not treated by electron beam irradiation.

[0100] Comparative Example 3

[0101] A fully polyethylene composite film, which is different from that of Example 1 in that the raw materials of the intermediate layer do not include silicone and the intermediate layer is not treated by electron beam irradiation at the same time.

[0102] Performance detection test

[0103] 1. Barrier performance: The oxygen transmission rate was tested by the coulometer detection method according to the standard "GB_T 19789-2005 Packaging materials, plastic films and sheets - Test method for oxygen transmission".

[0104] 2. Antibacterial performance: The antibacterial performance was tested with reference to QB / T 2591-2003 "Antibacterial plastics - Test methods for antibacterial properties and antibacterial effects" (film sticking method). The test bacteria were Escherichia coli and Staphylococcus aureus. The film samples were placed at room temperature and left standing for 10 d, then washed, dried and tested.

[0105] 3. Antioxidant property: A 0.02 mg / mL solution of 1,1-diphenyl-2-picrylhydrazyl (DPPH) was prepared with absolute ethanol. Samples of Examples 1-13 and Comparative Examples 1-3 were taken and punched into discs with a diameter of 10 mm. The sample discs were respectively added to 10 mL of DPPH solution and magnetically stirred at room temperature for 30 min, then the supernatant was taken to measure the absorbance at 517 nm. The scavenging rate of the sample on DPPH radicals was calculated by the following formula: Scavenging rate of DPPH radicals = (A0 - A1) / A0 × 100%; A0 is the absorbance without adding the sample; A1 is the absorbance after adding the sample.

[0106] 4. Wear resistance test: A Taber 1700 single turntable abrasion tester is used. A film sample (width: 10 mm, length: 180 mm) is clamped onto the rotating turntable platform with the surface layer facing up and the inner layer facing down, i.e., the surface layer is in contact with the grinding wheel. A 500-gram weight is installed as the wear test pressure, and S42 type sandpaper is installed on the grinding wheel. The rotation speed of the turntable platform holding the film sample is controlled at 72 rpm. The original gram weight m0 of the film before the wear test and the gram weight m1 of the film after the wear test are measured, and the wear amount △m = m0 - m1.

[0107] 5. The interlayer bonding performance is determined according to Method A in "GB / T 8808 1988 Test Method for Peel Strength of Soft Composite Plastic Materials", and a BLD-200H electronic peel tester is used to measure the peel strength between the surface layer and the inner layer of each specimen.

[0108] Experimental objects: The composite films prepared in Examples 1-14 and Comparative Examples 1-3 are used as experimental objects to conduct the above experiments respectively.

[0109] Table 1

[0110]

[0111]

[0112] Combined with Examples 1-13 and Table 1, it can be seen that the composite film prepared by three-layer compounding of the surface layer, intermediate layer and base layer in this application has good antioxidant properties, barrier properties, antibacterial properties and interlayer stability, ensuring good barrier and antibacterial properties of the composite food packaging film while effectively improving the stability of the film.

[0113] Among them, combined with Examples 1-4 and Table 1, it can be seen that when the surface layer, intermediate layer and base layer are compounded with specific proportional thicknesses, the oxygen barrier performance of the composite film can be improved, thereby maintaining the freshness and nutritional value of the items in the package. Combined with Examples 4-9 and Table 1, it can be seen that the oxygen transmission rate and the scavenging rate of DPPH free radicals in Examples 8-9 are significantly higher than those in Examples 4-7, indicating that when the antioxidant is 2,6-tert-butyl-4-methylphenol or bis(2-thienyl) disulfide, the antioxidant performance of the composite film can be further improved.

[0114] Combined with Examples 1-14 and Comparative Examples 1-3, and with reference to Table 1, it can be seen that the antioxidant and antibacterial properties of Examples 1-14 are significantly better than those of Comparative Examples 1-3. After introducing silicone into the intermediate layer of the composite film, the antioxidant and antibacterial properties of the composite film can be further improved; and when the intermediate layer is treated with electron beam radiation, not only can the interlayer stability of the composite film be effectively improved, but also the barrier properties of the composite film can be further enhanced. The antioxidant and antibacterial properties of Examples 13-14 are better than those of Examples 10-12, indicating that when the silicone used in this application is 3-aminopropyltriethoxysilane or aminomethyltrimethylsilane, the antibacterial and antioxidant properties of the composite film can be further improved.

[0115] This specific embodiment is only an explanation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications to this embodiment without creative contributions according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A fully polyethylene composite film, characterized in that, the composite film comprises a surface layer, an intermediate layer and a base layer. The raw materials of the surface layer include high-density polyethylene and an antioxidant; the raw materials of the intermediate layer include low-density polyethylene, a quaternary ammonium salt antibacterial agent and silicone; the raw materials of the base layer include high-molecular-weight polyethylene. After the intermediate layer is treated by electron beam radiation, the surface layer, the intermediate layer and the base layer are compounded to obtain the composite film. When the intermediate layer is treated by electron beam radiation, the temperature is 50 - 80 °C, the pressure is 100 - 300 kPa, the radiation dose is 5 - 8 kGy, and the treatment time is 10 - 15 min. The raw materials of the intermediate layer include: 80 - 100 parts of low-density polyethylene, 0.1 - 0.2 parts of a quaternary ammonium salt antibacterial agent and 2 - 8 parts of silicone. The quaternary ammonium salt antibacterial agent is benzalkonium chloride, didodecyldimethylammonium chloride, dodecyltrimethylammonium chloride or benzalkonium bromide. The silicone is methyltrimethylsiloxysilane, vinyltrimethoxysilane, γ-glycidyltrimethoxysilane, 3-aminopropyltriethoxysilane or aminomethyltrimethylsilane.

2. A fully polyethylene composite film according to claim 1, characterized in that: the thickness of the surface layer is 16 - 20 μm, the thickness of the intermediate layer is 28 - 32 μm, and the thickness of the base layer is 38 - 42 μm.

3. A fully polyethylene composite film according to claim 1, characterized in that: the melt index of the low-density polyethylene is 0.5 - 1.3 g / 10 min, and the density is 0.915 - 0.925 g / cm³; the melt index of the high-density polyethylene is 1.2 - 1.5 g / 10 min, and the density is 0.942 - 0.956 g / cm³; the melt index of the high-molecular-weight polyethylene is 0.1 - 0.4 g / 10 min, and the density is 0.932 - 0.948 g / cm³.

4. A fully polyethylene composite film according to claim 1, characterized in that: the antioxidant is a hindered phenol antioxidant.

5. A fully polyethylene composite film according to claim 4, characterized in that: the hindered phenol antioxidant is 2,6-tert-butyl-4-methylphenol or bis(2-thienyl) disulfide.

6. A method for preparing a fully polyethylene composite film according to any one of claims 1 - 5, characterized in that: the preparation comprises the following steps: Preparing the surface layer: Mix high-density polyethylene and an antioxidant, and prepare the surface layer by melt blending. Preparing the intermediate layer: First, mix and stir the quaternary ammonium salt antibacterial agent and silicone at 60 - 80 °C and a stirring speed of 50 - 150 revolutions per minute, then mix with low-density polyethylene, prepare the intermediate layer by melt blending, and then perform electron beam radiation treatment on the intermediate layer. Preparing the base layer: Prepare the base layer by melt blending high-molecular-weight polyethylene. Compounding: Stack the surface layer, the intermediate layer and the base layer in sequence, and compound each layer together by hot pressing to obtain the composite film.

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