A method for producing a polyethylene blown film for fruit and vegetable packaging

Abstract

The application discloses a preparation method of a polyethylene blown film for fruit and vegetable packaging, and comprises the following steps: introducing a first outer layer material, an inner layer material and a second outer layer material into hoppers of a three-layer co-extrusion blowing machine respectively to perform three-layer co-extrusion blowing, and then performing traction treatment to obtain the polyethylene blown film for fruit and vegetable packaging; the first outer layer material and the second outer layer material are linear low-density polyethylene; and the inner layer material is low-density polyethylene; and the application effectively improves the heat resistance of the film through structural design and material modification, and meanwhile, good oxygen isolation performance is obtained.

Description

Technical Field

[0001] This invention belongs to the field of polyethylene film technology, and specifically relates to a method for preparing polyethylene blown film for fruit and vegetable packaging. Background Technology

[0002] Polyethylene film has the advantages of excellent chemical stability, heat sealability and low price, making it one of the most widely used materials in agricultural covering and industrial production. According to its different application scenarios, polyethylene film can be roughly divided into two categories: general-purpose film and functional film. General-purpose film mainly includes agricultural polyethylene film and packaging polyethylene film, while functional film is film used in specific scenarios, such as battery separator, anti-rust film, ion exchange membrane, etc.

[0003] Polyethylene (PE) is widely used for packaging various foods, meats, vegetables, and other agricultural products due to its non-toxic and odorless properties, good open-ended and heat-sealing properties, good transparency, and the ability to print text and patterns on it. While PE packaging films are convenient and easy to use, they only offer some barrier properties against water vapor and lack sufficient barrier properties against gases such as oxygen and carbon dioxide, limiting their application in more demanding packaging fields. Therefore, the development and preparation of high-barrier PE films has attracted considerable attention. Current research methods can be broadly categorized into two types: the first involves incorporating and fixing additives into the polymer film to achieve high barrier properties, and the second employs multilayer composite processes to prepare composite films with even better barrier properties.

[0004] Chinese patent (publication number CN118560132A) discloses an antibacterial polyethylene blown film, its preparation method, and its application. This polyethylene blown film is formed by co-extrusion blow molding of three layers: an inner layer, a middle layer, and an outer layer. The inner layer material contains an antibacterial masterbatch, which is either a silver-zinc ion antibacterial masterbatch or an oyster shell powder antibacterial masterbatch. The weight of the antibacterial masterbatch in the inner layer material is 3-8% of the weight of the polyethylene. While this invention uses a three-layer co-extrusion blow molding process to obtain a polyethylene film, it lacks research on the interlayer properties of different materials. Furthermore, the heat resistance and oxygen barrier properties of the polyethylene film need further improvement.

[0005] Therefore, how to select different polyethylenes as inner and outer layer materials, carry out corresponding modification treatments, and combine them with traction treatment and other processes to prepare polyethylene blown films for fruit and vegetable packaging, effectively increasing the thermal decomposition temperature of the film while reducing oxygen permeability, has become a research direction. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing polyethylene blown film for fruit and vegetable packaging. The present invention uses montmorillonite linear low-density polyethylene composite as the outer layer material and plasma-treated low-density polyethylene as the inner layer material. The polyethylene blown film is obtained through co-extrusion blow molding combined with traction treatment. Through structural design and material modification, the heat resistance of the film is effectively improved, while good oxygen barrier properties are obtained, enabling it to be better applied in the field of fruit and vegetable packaging.

[0007] The technical solution of the present invention is as follows:

[0008] This invention provides a method for preparing polyethylene blown film for fruit and vegetable packaging, comprising the following steps:

[0009] The first outer layer material, the inner layer material, and the second outer layer material are respectively fed into the hopper of the three-layer co-extrusion blow molding machine for three-layer co-extrusion blow molding, and then subjected to traction processing to obtain polyethylene blown film for fruit and vegetable packaging.

[0010] The first outer layer material and the second outer layer material are montmorillonite-modified linear low-density polyethylene; the preparation method of the montmorillonite-modified linear low-density polyethylene includes: firstly, intercalating sodium-based montmorillonite with a long-chain quaternary ammonium salt to obtain quaternary ammonium salt-modified montmorillonite; then, melt-blending linear low-density polyethylene, a compatibilizer, and the quaternary ammonium salt-modified montmorillonite to obtain a montmorillonite / linear low-density polyethylene composite.

[0011] The inner layer material is low-density polyethylene.

[0012] This invention uses sodium-based montmorillonite as raw material and modifies it by using long-chain quaternary ammonium salts to graft or intercalate organic segments into the lamellar layers of sodium-based montmorillonite, thereby obtaining quaternary ammonium salt-modified montmorillonite. This reduces the surface energy of montmorillonite and facilitates its distribution in a polyethylene matrix. At the same time, a compatibilizer, polyethylene grafted with maleic anhydride, is added to improve the compatibility of montmorillonite with linear low-density polyethylene. The montmorillonite / linear low-density polyethylene composite is obtained by melt blending.

[0013] As a preferred technical solution of the present invention, the intercalation modification step is as follows: by weight, 4-6 parts of sodium-based montmorillonite are added to 90-100 parts of deionized water and stirred to disperse to obtain a montmorillonite dispersion; under conditions of 70-80°C, 3-5 parts of long-chain quaternary ammonium salt are added to 30-40 parts of deionized water and mixed evenly, and then added to the montmorillonite dispersion and stirred at high speed for 4-6 hours, followed by post-treatment to obtain quaternary ammonium salt modified montmorillonite.

[0014] As a preferred embodiment of the present invention, the sodium-based montmorillonite can be in the following weight proportions: 4 parts, 4.5 parts, 5 parts, 5.5 parts, or 6 parts, etc.

[0015] As a preferred embodiment of the present invention, the weight parts of the long-chain quaternary ammonium salt can be 3 parts, 3.5 parts, 4 parts, 4.5 parts, or 5 parts, etc.

[0016] As a preferred technical solution of the present invention, the post-processing steps are: vacuum filtration, washing with deionized water, vacuum drying, and ball milling.

[0017] As a preferred embodiment of the present invention, the long-chain quaternary ammonium salt is selected from hexadecyltrimethylammonium bromide or octadecyltrimethylammonium chloride.

[0018] As a preferred embodiment of the present invention, the compatibilizer is polyethylene grafted with maleic anhydride.

[0019] As a preferred technical solution of the present invention, the melt blending step is as follows: 400-500 parts of linear low-density polyethylene, 15-25 parts of compatibilizer and 25-35 parts of the quaternary ammonium salt modified montmorillonite are melt-extruded, traction-driven and water-cooled granulation is performed.

[0020] As a preferred embodiment of the present invention, the linear low-density polyethylene may be in the following weight proportions: 400 parts, 420 parts, 440 parts, 460 parts, 480 parts, or 500 parts, etc.

[0021] As a preferred embodiment of the present invention, the compatibilizer may be present in weight parts of 15, 17, 19, 21, 23, or 25 parts, etc.

[0022] As a preferred embodiment of the present invention, the compatibilizer may be present in weight parts of 25, 27, 29, 31, 33, or 35 parts, etc.

[0023] In the melt blending process of the montmorillonite / linear low-density polyethylene composite of the present invention, due to the good compatibility between quaternary ammonium salt modified montmorillonite and linear low-density polyethylene, the quaternary ammonium salt modified montmorillonite can be uniformly dispersed in the resin matrix. The polyethylene molecular chains enter into the modified montmorillonite sheets and are gradually peeled off. The peeled montmorillonite nanosheets have good gas barrier properties for gas molecules such as oxygen, thereby effectively reducing oxygen permeability. At the same time, the montmorillonite nanosheets can form a dense barrier in polyethylene, effectively hindering the rapid transfer of heat, delaying the rise of matrix temperature, and capturing and inhibiting small molecule volatile products generated during polymer thermal decomposition, significantly increasing the thermal decomposition temperature of the material.

[0024] As a preferred embodiment of the present invention, the low-density polyethylene is plasma-treated low-density polyethylene.

[0025] As a preferred embodiment of the present invention, the plasma treatment conditions are as follows: low-density polyethylene is placed in a plasma treatment system, oxygen is used as the working gas, the oxygen volume flow rate is 0.008~0.010L / min, the ionization power is 200~220W, and the treatment time is 2~3min.

[0026] The inner layer material of this invention uses plasma-treated low-density polyethylene. High-energy particles in the plasma bombard the surface of low-density polyethylene to break CH and CC bonds, generating a large number of free radicals on the low-density polyethylene molecular chain. Then, in an oxygen atmosphere, a reaction occurs to introduce oxygen-containing functional groups. These functional groups contain electronegative atoms or are directly negatively charged, making the surface of the low-density polyethylene exhibit overall negative charge.

[0027] As a preferred technical solution of the present invention, the conditions for the traction treatment are: the lateral and longitudinal traction ratio is 3×3, the traction temperature is 118~120℃, the traction speed is 90~100mm / s, and the cooling time is 10~15s.

[0028] The outer layer of the film material of this invention is linear low-density polyethylene (LLDPE) with short-chain branched polyethylene, and the inner layer is low-density polyethylene (LDPE) with long-chain branched polyethylene. During the traction process, the short-chain branched polyethylene has a fast orientation crystallization rate, while the long-chain branched polyethylene has a slow orientation crystallization rate. This results in an interfacial layer that influences each other due to the difference in response. In the interfacial layer, the short-chain branched polyethylene molecular chain segments form more crystallization precursors, which induce the orientation crystallization of the long-chain branched polyethylene. The high crystallinity of the interfacial layer improves the overall performance of the polyethylene blown film.

[0029] As a preferred embodiment of the present invention, the thickness of the first outer layer and the second outer layer is 20~40μm, and the thickness of the inner layer is 30~50μm.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The polyethylene blown film for fruit and vegetable packaging of the present invention uses montmorillonite linear low-density polyethylene composite as the outer layer material and plasma-treated low-density polyethylene as the inner layer material. It is co-extruded and blown, and combined with traction treatment. With structural design and material modification, it obtains good heat resistance and oxygen barrier properties.

[0032] (2) In the melt blending process of the montmorillonite / linear low-density polyethylene composite of the present invention, due to the good compatibility between quaternary ammonium salt modified montmorillonite and linear low-density polyethylene, the quaternary ammonium salt modified montmorillonite can be uniformly dispersed in the resin matrix, and the polyethylene molecular chains enter into the modified montmorillonite sheets and gradually peel them off. The peeled montmorillonite nanosheets have good gas barrier properties for gas molecules such as oxygen, thereby effectively reducing the oxygen permeability; at the same time, the montmorillonite nanosheets can form a dense barrier in polyethylene, effectively hindering the rapid transfer of heat, delaying the rise of matrix temperature, and capturing and hindering the small molecule volatile products generated during the thermal decomposition of polymer, significantly increasing the thermal decomposition temperature of the material.

[0033] (3) The inner layer material of the present invention exhibits negative charge on the surface of low-density polyethylene after plasma treatment, while the montmorillonite / linear low-density polyethylene composite achieves cationization of the outer layer material through quaternary ammonium salt modification. During the material composite process, the inner layer material and the outer layer material can electrostatically bond at the interface, thereby forming an electrostatic composite network at the interface layer, effectively increasing the thermal decomposition temperature and reducing the oxygen permeability.

[0034] (4) The interface layer of the present invention has a dual network structure. The first network structure is formed by the physical entanglement of the molecular chains of the outer short-branched polyethylene and the inner long-branched polyethylene during the stretching process. The second network structure is formed by the electrostatic bonding of the inner and outer materials in the interface layer. The network structure can change the heat transfer path in the polyethylene film, effectively blocking heat conduction, improving the thermal stability and thermal decomposition temperature of the material. At the same time, the formation of the interface network structure reduces the free volume in the polyethylene film, increasing the difficulty of oxygen molecule penetration, thereby reducing the oxygen permeability. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the molecular chain of linear low-density polyethylene (LLDPE).

[0037] Figure 2 This is a schematic diagram of the molecular chain of low-density polyethylene (LDPE).

[0038] Figure 3 The image shows the XRD pattern of the quaternary ammonium salt modified montmorillonite in Example 1.

[0039] Figure 4This is a schematic diagram of the polyethylene blown film structure in Example 1. Detailed Implementation

[0040] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0041] The sources of some components in the examples and comparative examples are as follows:

[0042] Linear low-density polyethylene (LLDPE), grade 5110G, short-chain polyethylene, density 0.926 g / cm³ 3 Melt index MI 0.85 g / 10 min (2.16 kg, 190°C), weight average relative molecular weight 140,000, purchased from DuPont Dow Chemical Company;

[0043] Low-density polyethylene (LDPE), grade 2420D, is a long-chain branched polyethylene with a density of 0.922 g / cm³. 3 Melt index MI 0.25 g / 10 min (2.16 kg, 190°C), weight average relative molecular weight 180,000, purchased from China Petroleum Daqing Petrochemical Co., Ltd.

[0044] Sodium-based montmorillonite, product number P766867, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0045] Hexadecyltrimethylammonium bromide, CAS No. 57-09-0, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0046] Octadecyltrimethylammonium chloride, CAS No. 112-03-8, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0047] Polyethylene grafted with maleic anhydride, product number M87824, purchased from Shanghai Mairui Biochemical Technology Co., Ltd. Example 1

[0048] This embodiment provides a method for preparing polyethylene blown film for fruit and vegetable packaging, including the following steps:

[0049] The first outer layer material, the inner layer material, and the second outer layer material are respectively fed into the hopper of a three-layer co-extrusion blow molding machine for three-layer co-extrusion blow molding. Then, traction processing is performed (the lateral and longitudinal traction ratio is 3×3, the traction temperature is 120℃, the traction speed is 100mm / s, and the cooling time is 10s) to obtain a polyethylene blown film for fruit and vegetable packaging (the thickness of the first and second outer layers is 40μm, and the thickness of the inner layer is 50μm).

[0050] The first and second outer layer materials are montmorillonite-modified linear low-density polyethylene. The preparation of the montmorillonite-modified linear low-density polyethylene involves: adding 6 parts by weight of sodium-based montmorillonite to 100 parts by weight of deionized water and stirring to obtain a montmorillonite dispersion; adding 5 parts by weight of long-chain quaternary ammonium salt hexadecyltrimethylammonium bromide to 40 parts by weight of deionized water at 80°C and mixing thoroughly, then adding the mixture to the montmorillonite dispersion and stirring at high speed for 6 hours; filtering under reduced pressure, washing with deionized water, vacuum drying, and ball milling to obtain quaternary ammonium salt-modified montmorillonite; and then melt-extruding 500 parts by weight of linear low-density polyethylene, 25 parts by weight of compatibilizer polyethylene grafted with maleic anhydride, and 35 parts by weight of the quaternary ammonium salt-modified montmorillonite, followed by traction and water-cooled granulation to obtain a montmorillonite / linear low-density polyethylene composite.

[0051] The inner layer material is plasma-treated low-density polyethylene; the plasma treatment conditions are as follows: the low-density polyethylene is placed in the plasma treatment system, oxygen is used as the working gas, the oxygen volume flow rate is 0.010 L / min, the ionization power is 220 W, and the treatment time is 2 min. Example 2

[0052] This embodiment provides a method for preparing polyethylene blown film for fruit and vegetable packaging, including the following steps:

[0053] The first outer layer material, the inner layer material, and the second outer layer material are respectively fed into the hopper of a three-layer co-extrusion blow molding machine for three-layer co-extrusion blow molding. Then, traction processing is performed (the lateral and longitudinal traction ratio is 3×3, the traction temperature is 118℃, the traction speed is 90mm / s, and the cooling time is 15s) to obtain a polyethylene blown film for fruit and vegetable packaging (the thickness of the first and second outer layers is 20μm, and the thickness of the inner layer is 30μm).

[0054] The first and second outer layer materials are montmorillonite-modified linear low-density polyethylene. The preparation of the montmorillonite-modified linear low-density polyethylene is as follows: by weight, 4 parts of sodium-based montmorillonite are added to 90 parts of deionized water and stirred to disperse to obtain a montmorillonite dispersion; 3 parts of octadecyltrimethylammonium chloride are added to 30 parts of deionized water at 70°C and mixed evenly, then added to the montmorillonite dispersion and stirred at high speed for 4 hours, filtered under reduced pressure, washed with deionized water, vacuum dried, and ball-milled to obtain quaternary ammonium salt-modified montmorillonite; 400 parts of linear low-density polyethylene, 15 parts of compatibilizer polyethylene grafted with maleic anhydride, and 25 parts of the quaternary ammonium salt-modified montmorillonite are melt-extruded, drawn, and water-cooled granulated to obtain a montmorillonite / linear low-density polyethylene composite.

[0055] The inner layer material is plasma-treated low-density polyethylene; the plasma treatment conditions are as follows: the low-density polyethylene is placed in the plasma treatment system, oxygen is used as the working gas, the oxygen volume flow rate is 0.008 L / min, the ionization power is 200 W, and the treatment time is 3 min. Example 3

[0056] This embodiment provides a method for preparing polyethylene blown film for fruit and vegetable packaging, including the following steps:

[0057] The first outer layer material, the inner layer material, and the second outer layer material are respectively fed into the hopper of a three-layer co-extrusion blow molding machine for three-layer co-extrusion blow molding. Then, traction processing is performed (the lateral and longitudinal traction ratio is 3×3, the traction temperature is 119℃, the traction speed is 95mm / s, and the cooling time is 12s) to obtain a polyethylene blown film for fruit and vegetable packaging (the thickness of the first and second outer layers is 30μm, and the thickness of the inner layer is 40μm).

[0058] The first and second outer layer materials are montmorillonite-modified linear low-density polyethylene. The preparation of the montmorillonite-modified linear low-density polyethylene is as follows: by weight, 5 parts of sodium-based montmorillonite are added to 95 parts of deionized water and stirred to disperse to obtain a montmorillonite dispersion; under 75°C, 4 parts of long-chain quaternary ammonium salt hexadecyltrimethylammonium bromide are added to 35 parts of deionized water and mixed evenly, then added to the montmorillonite dispersion and stirred at high speed for 5 hours, filtered under reduced pressure, washed with deionized water, vacuum dried, and ball-milled to obtain quaternary ammonium salt-modified montmorillonite; 450 parts of linear low-density polyethylene, 20 parts of compatibilizer polyethylene grafted with maleic anhydride, and 30 parts of the quaternary ammonium salt-modified montmorillonite are melt-extruded, drawn, and water-cooled granulated to obtain a montmorillonite / linear low-density polyethylene composite.

[0059] The inner layer material is plasma-treated low-density polyethylene; the plasma treatment conditions are as follows: the low-density polyethylene is placed in the plasma treatment system, oxygen is used as the working gas, the oxygen volume flow rate is 0.009 L / min, the ionization power is 210 W, and the treatment time is 2 min.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that linear low-density polyethylene (grade 5110G) was used instead of montmorillonite-modified linear low-density polyethylene as the first and second outer layer materials.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that low-density polyethylene (grade 2420D) was used instead of plasma-treated low-density polyethylene.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that no traction treatment is performed after co-extrusion blow molding.

[0066] The performance of the above embodiments and comparative examples was tested using the following methods:

[0067] Haze test: The test shall be conducted in accordance with the requirements of ASTM D1003-2013 Test Method for Transmittance and Haze of Transparent Plastics.

[0068] Thermal decomposition temperature test: The thermal decomposition temperature (5% Td, temperature at which 5% mass loss) of the film was determined using a thermogravimetric analyzer (model TGA55, TA Instruments, USA) at a heating rate of 20℃ / min from room temperature to 600℃.

[0069] Oxygen transmission rate test: The test shall be conducted in accordance with the requirements of ASTM D3985-17 Standard Test Method for Measuring the Oxygen Transmission Rate Through Plastic Films and Sheets Using Coulomb Sensors.

[0070] The performance test data above are shown in Table 1.

[0071] Table 1 Performance Test Results

[0072] Haze% Thermal decomposition temperature (5% Td) ℃ Oxygen permeability (cm³ / (m²·24h·atm)) Example 1 3.5 422 394 Example 2 2.9 419 411 Example 3 3.2 420 403 Comparative Example 1 3.6 383 685 Comparative Example 2 3.1 395 622 Comparative Example 3 2.8 404 574

[0073] As can be seen from the above, the present invention uses montmorillonite linear low-density polyethylene composite as the outer layer material and plasma-treated low-density polyethylene as the inner layer material. The polyethylene blown film is obtained by co-extrusion blow molding and traction treatment. The heat resistance of the film is effectively improved through structural design and material modification, while obtaining good oxygen barrier properties (Examples 1 to 3).

[0074] Compared to Example 1, using linear low-density polyethylene (grade 5110G) instead of montmorillonite-modified linear low-density polyethylene as the first and second outer layer materials, the lack of quaternary ammonium salt-modified montmorillonite resulted in a lower film thermal decomposition temperature and poorer oxygen barrier performance (Comparative Example 1); compared to Example 1, using low-density polyethylene (grade 2420D) instead of plasma-treated low-density polyethylene, the lack of plasma treatment prevented the formation of an electronegative interfacial layer, resulting in a lower film thermal decomposition temperature and poorer oxygen barrier performance (Comparative Example 2); compared to Example 1, without traction treatment, the lack of an interfacial layer affected the formation of the dual network structure, resulting in a lower film thermal decomposition temperature and poorer oxygen barrier performance (Comparative Example 3).

Claims

1.A method for preparing a polyethylene blown film for fruit and vegetable packaging, characterized in that, comprising the following steps: introducing a first outer layer material, an inner layer material and a second outer layer material into hoppers of a three-layer co-extrusion blowing machine respectively to form a sheet by three-layer co-extrusion blowing, and performing a traction treatment on the sheet to obtain the polyethylene blown film for fruit and vegetable packaging; the first outer layer material and the second outer layer material are montmorillonite modified linear low density polyethylene; the method for preparing the montmorillonite modified linear low density polyethylene comprises: first using a long-chain quaternary ammonium salt to intercalate modify sodium-based montmorillonite to obtain quaternary ammonium salt modified montmorillonite; and then melt blending linear low density polyethylene, a compatibilizer and the quaternary ammonium salt modified montmorillonite to obtain a montmorillonite / linear low density polyethylene composite; the traction treatment is performed under the following conditions: a horizontal and vertical traction ratio of 3×3, a traction temperature of 118-120 ℃, a traction speed of 90-100 mm / s, and a cooling time of 10-15 s; the step of intercalation modification comprises: adding 4-6 parts of sodium-based montmorillonite to 90-100 parts of deionized water to obtain a montmorillonite dispersion liquid by stirring and dispersing; adding 3-5 parts of a long-chain quaternary ammonium salt to 30-40 parts of deionized water at 70-80 ℃, mixing uniformly, and then adding to the montmorillonite dispersion liquid and stirring at a high speed for 4-6 h, followed by post-treatment to obtain quaternary ammonium salt modified montmorillonite; the long-chain quaternary ammonium salt is selected from cetyltrimethylammonium bromide or octadecyltrimethylammonium chloride; the step of melt blending comprises: melt extruding 400-500 parts of linear low density polyethylene, 15-25 parts of a compatibilizer and 25-35 parts of the quaternary ammonium salt modified montmorillonite, and then performing traction and water cooling to obtain granules; the low density polyethylene is plasma treated low density polyethylene; and the inner layer material is low density polyethylene. 2.The method for preparing a polyethylene blown film for fruit and vegetable packaging according to claim 1, characterized in that, the compatibilizer is polyethylene grafted maleic anhydride. 3.The method for preparing a polyethylene blown film for fruit and vegetable packaging according to claim 1, characterized in that, the plasma treatment is performed under the following conditions: the low density polyethylene is placed in a plasma treatment system, oxygen is used as the working gas, the oxygen volume flow rate is 0.008-0.010 L / min, the ionization power is 200-220 W, and the treatment time is 2-3 min. 4.The method for preparing a polyethylene blown film for fruit and vegetable packaging according to claim 1, characterized in that, the thickness of the first outer layer and the second outer layer is 20-40 μm, and the thickness of the inner layer is 30-50 μm. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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