A method for producing a polyethylene film

Abstract

This invention discloses a method for preparing polyethylene film and its applications, relating to the field of chemical product manufacturing technology. The preparation method includes: preparing a mixed slurry with a solvent having an open flash point of 50–150 °C and polyethylene resin; obtaining a polyethylene sheet melt through a screw extruder; subjecting the polyethylene sheet melt to initial stretching in a selected medium environment; by selecting the medium environment and controlling the stretching residence time, preventing structural collapse in the nascent film and retaining the solvent, thus obtaining a nascent polyethylene film; and subjecting the nascent polyethylene film to secondary stretching and heat setting to obtain a polyethylene film. The technical method provided by this invention offers strong controllability, enabling the preparation of products with thicknesses of 0.5–400 μm, porosities of 50–95%, and air permeability of 1–100,000 s / 100 mL through parameter adjustment. These products can be applied in fields such as medical packaging, food packaging, safety protection, precision electronic packaging, lithium-ion battery separators, and microfiltration / nanofiltration separation.

Description

Technical Field

[0001] This invention relates to the field of chemical product manufacturing technology, and specifically to a method for preparing polyethylene film. Background Technology

[0002] Polyethylene (PE) is a thermoplastic resin produced by the polymerization of ethylene monomers. Due to its excellent mechanical strength, chemical stability, corrosion resistance, and biocompatibility, polyethylene film has broad application prospects in many fields, including lithium battery separators, electronic packaging, food packaging, and environmental protection leak-proofing.

[0003] When polyethylene is processed into applications such as lithium-ion battery separators, its preparation process is a wet film-forming process. This process uses high-boiling-point white oil as a solvent to prepare the nascent film, which is then removed through biaxial stretching and multi-stage extraction to finally obtain a microporous film. Although the separators prepared by this process have uniform pore size distribution and excellent overall mechanical strength, and currently hold an absolute dominant position in the lithium-ion battery separator market, in actual large-scale production, due to the difficulty in volatile white oil, a large amount of volatile organic solvent must be used for repeated elution, double diffusion, and negative pressure drying after film formation to obtain a porous polyethylene film. Furthermore, the white oil has a weak solubility for polyethylene and low melt strength, resulting in a low stretching ratio of the nascent film and difficulty in increasing porosity (not exceeding 50%). In addition, the problem of solvent residue is difficult to completely solve through extraction processes. Residual solvent affects the chemical stability of the membrane, limiting its application in fields with high purity requirements such as food, pharmaceuticals, and electronics. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing polyethylene film.

[0005] The core technical points of the polyethylene film preparation method provided by the present invention include: selecting an organic solvent with an open flash point in the range of 50~150℃ as the solvent for preparing the film slurry; and effectively controlling the occupancy effect and pore-forming behavior of the solvent in the nascent film by selecting the medium environment of the stretching process and controlling the stretching residence time, thereby achieving controllable preparation of the polyethylene film porosity.

[0006] This method, through the synergistic control of solvent removal rate and structural stability, can flexibly prepare polyethylene films suitable for medical packaging, food packaging, safety protection, precision electronic packaging, lithium-ion battery separators, and microfiltration and nanofiltration separation, according to the differentiated air permeability requirements of different application scenarios. It has the significant advantages of strong process controllability and a wide range of adjustable product performance.

[0007] The method for preparing polyethylene film provided by the present invention includes the following steps: 1) Prepare a mixed slurry by mixing a solvent with an open flash point of 50-150 °C and polyethylene resin; then adjust the slurry temperature to the preset temperature range. 2) The mixed slurry obtained in step 1) is extruded through a screw extruder to obtain polyethylene sheet melt; 3) The polyethylene sheet melt obtained in step 2) is initially stretched in a medium environment. By selecting the medium environment and controlling the stretching residence time, the nascent film does not undergo structural collapse and retains the solvent, thus obtaining a nascent polyethylene film. 4) The polyethylene nascent film obtained in step 3) is stretched a second time, and then heat-set to obtain a polyethylene film with the required porosity.

[0008] According to an alternative embodiment of the present invention, when a large amount of solvent is retained in the stubble and no structural collapse occurs before secondary stretching (which can be controlled by adjusting the total stretching residence time in the gas medium), a porous polyethylene film with a porosity in the range of 50% to 95% can be formed after secondary stretching; similarly, when a large amount of solvent is rapidly removed from the stubble, but structural collapse can still be avoided before secondary stretching, a porous polyethylene film with a porosity in the range of 50% to 95% can also be obtained.

[0009] Therefore, preferably, when the desired final polyethylene film porosity is in the range of 50% to 95%, the medium used in the drawing process is selected from one of the following medium forms: a. The stretching process involves only a gaseous medium; b. The stretching process involves only a liquid medium; c. The stretching process first passes through a gaseous medium and then through a liquid medium; d. The stretching process first passes through a liquid medium, then a gaseous medium, and finally back to a liquid medium; e. The stretching process first passes through a gaseous medium, then a liquid medium, and then back through a gaseous medium.

[0010] In any of the aforementioned media forms, the total stretching residence time of the polyethylene sheet melt in the gaseous medium is controlled to be less than 5 minutes, thereby preparing a polyethylene film with a porosity in the range of 50% to 95%. If the selected media form requires passing through multiple gaseous medium stages, the total stretching residence time in the gaseous medium as referred to in this invention means the sum of the stretching residence times in all gaseous media.

[0011] The polyethylene film with a porosity ranging from 50% to 95% obtained by this invention can achieve rapid electrolyte wetting and efficient ion transport due to its high porosity (suitable for the high-rate charge and discharge requirements of power batteries), ensuring battery cycle life and safety, and can be applied in the field of lithium-ion battery separators. It can also achieve nanofiltration or microfiltration films with adjustable pore size and uniformity of pore distribution through pore size control, and can be applied in the fields of nanofiltration and microfiltration separation.

[0012] According to a preferred embodiment of the present invention, a polyethylene film with a porosity of more than 80% (80%~95% porosity) is further prepared by controlling the total stretching residence time of the polyethylene sheet melt in the gas medium to be less than 3 minutes.

[0013] According to a preferred embodiment of the present invention, the liquid medium includes one or more of water, anhydrous ethanol, n-hexane, n-heptane, dichloromethane, n-pentane, petroleum ether, diethylamine, and hexadiene, and the gaseous medium includes one or more of air, carbon dioxide, nitrogen, helium, neon, argon, krypton, and xenon.

[0014] The liquid medium selected in this invention must be immiscible with the solvent in the mixed slurry. For example, when the solvent in the mixed slurry is decahydronaphthalene, water is the preferred liquid medium. During the initial drawing process of the polyethylene sheet melt entering the liquid medium, the liquid medium can form a liquid seal on the cooled polyethylene sheet to prevent the solvent contained in the polyethylene sheet from being easily removed during the initial drawing process. In some optional operations, the material may pass through a gaseous medium only during the initial drawing process, or it may pass through a gaseous medium before, after, or between two liquid media. However, it is necessary to strictly control the total drawing residence time in the gaseous medium, and the gaseous medium must be chemically stable, readily available, and not react with the solvent in the mixed slurry. Under the above gas purging, the desorption rate of the solvent in the mixed slurry from the polyethylene sheet will be accelerated. Therefore, it is necessary to control the residence time of the polyethylene sheet in the gaseous medium. Under the medium type, temperature, and drawing process selected in this invention, in order to obtain a polyethylene film with a porosity higher than 50%, the total drawing residence time of the ethylene sheet melt in the gaseous medium should be less than 5 minutes; in order to obtain a polyethylene film with a porosity higher than 80%, the total drawing residence time of the ethylene sheet melt in the gaseous medium should be less than 3 minutes.

[0015] According to a preferred embodiment of the present invention, the molecular weight of the polyethylene resin in step 1) is 1×10⁻⁶. 5 g / mol~1.0×10 7Within the range of g / mol; the solvent is tetrahydronaphthalene, decahydronaphthalene, solvent oil with an open flash point of 50~150℃, butyl lactate, indene, diethylene glycol butyl ether, tributyl phosphate, o-dichlorobenzene, 2,5-hexanedione, and N-methylpyrrolidone.

[0016] According to a preferred embodiment of the present invention, the mass concentration of the mixed slurry is 2 to 60 wt%; the preparation temperature of the mixed slurry is in the range of 50 to 115 ℃, and the preset temperature range is -40 to 50 ℃.

[0017] According to a preferred embodiment of the present invention, the preparation of the mixed slurry is carried out under stirring conditions or under ultrasonic vibration. The stirring conditions include a stirring speed of 60-200 rpm and a stirring preparation time of 0.1-4 hours. The duration of ultrasonic vibration is 0.5 to 120 minutes.

[0018] According to a preferred embodiment of the present invention, the screw extrusion equipment in step 2) includes a screw extruder, a melt filter, a melt metering pump, and a film die; the screw temperature of the screw extruder is in the range of 140 to 320 °C, the screw speed is in the range of 20 to 300 rpm, the melt pressure is in the range of 1 to 8 MPa, and the speed of the melt metering pump is in the range of 1 to 20 rpm.

[0019] According to a preferred embodiment of the present invention, the medium temperature in step 3) is -20 to 110 °C; the initial draw ratio is 1 to 20 times, and the initial draw speed is 0.1 to 20 m / min; the initial polyethylene film thickness is 1 to 2500 μm. Preferably, the medium temperature is 0 to 110 °C; more preferably, for a gaseous medium, the medium temperature is 0 to 70 °C, and for a liquid medium, the medium temperature is -20 to 150 °C.

[0020] According to a preferred embodiment of the present invention, the secondary stretching temperature in step 4) is in the range of 20 to 150 °C, the secondary stretching speed is in the range of 0.1 to 10 mm / s, and the stretching ratio is in the range of 2 to 576 times.

[0021] According to a preferred embodiment of the present invention, the heat setting temperature in step 4) is 60~125 ℃, and the heat setting time is 0.5~24 hours.

[0022] The beneficial effects of the present invention through the above technical solution are as follows: The method for preparing polyethylene film provided by this invention, compared with existing methods for preparing polyethylene film, can prepare high-throughput porous polyethylene film with a porosity of more than 50%. By adjusting the medium environment and controlling the stretching residence time, high-throughput porous polyethylene film with a porosity of more than 80% can be further prepared. With high porosity, rapid wetting of electrolyte and efficient ion transport are achieved, ensuring battery cycle life and safety, and can be applied in the field of lithium-ion battery separators.

[0023] In existing large-scale production of polyethylene film, high-boiling-point solvents are used as flow promoters during extrusion. Because these solvents are difficult to volatilize, a large amount of volatile organic solvent is required for double diffusion and negative pressure drying after film formation to obtain a porous polyethylene film. This process is lengthy, costly, and results in a porosity of less than 50%. The method for preparing polyethylene film provided by this invention eliminates the double diffusion process involving the film-forming organic solvent and a large amount of volatile organic solvent, shortening the process flow, reducing equipment investment costs, and lowering production costs. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] The present invention will be described in detail below through embodiments.

[0026] In the following examples and comparative examples: Molecular weight determination method: The molecular weight was determined by high-temperature column chromatography-gel chromatography at 160℃ using trichlorobenzene as a solvent.

[0027] Porosity determination method: According to GB / T 36363-2018, the porosity of polyethylene film is determined by density method without damaging the sample film.

[0028] Air permeability test method: According to GB / T 1038-2022, the air permeability of polyethylene film is determined by the pressure difference method.

[0029] Example 1 This embodiment illustrates the preparation of polyethylene film using the preparation method of the present invention.

[0030] 1) The molecular weight is 1.00×10 5Polyethylene (g / mol) and decahydronaphthalene (cup flash point 57 °C) were mixed at a concentration of 15 wt% and prepared at 95 °C and 100 rpm for 0.5 hours to form a slurry. Heating was then stopped, and the temperature was lowered to 23 °C while maintaining the stirring speed.

[0031] 2) The mixed slurry obtained in step 1) is passed through a screw extrusion device (including a screw extruder, melt filter, melt metering pump and film die) at an extrusion temperature of 180 ℃, a twin screw speed of 80 rpm, a metering pump speed of 10 rpm and a melt pressure of 2.5 MPa to obtain polyethylene sheet melt.

[0032] 3) The polyethylene sheet melt obtained in step 2) is first passed through a gaseous medium of air at 23 °C, and then through a liquid medium of water at 10 °C. The stretching rate during this process is 0.1 m / min, and the residence time in air at 23 °C is 1 minute, to obtain a polyethylene nascent film.

[0033] 4) The polyethylene nascent film obtained in step 3) is subjected to secondary stretching in an air atmosphere at 110 ℃, at a stretching rate of 0.1 mm / s and a stretching ratio of 576 times, and then heat-set at 60 ℃ for 0.5 hours to obtain polyethylene film S1.

[0034] The polyethylene film S1 obtained in Example 1 was tested for thickness and porosity. The thickness data is shown in Table 1 and the porosity data is shown in Table 2.

[0035] Example 2 This embodiment illustrates the preparation of polyethylene film using the preparation method of the present invention.

[0036] 1) The molecular weight is 1.00×10 7 Polyethylene (g / mol) and decahydronaphthalene (cup flash point 57 °C) were mixed at a concentration of 2 wt% and prepared at 115 °C and 60 rpm for 0.1 hours to form a slurry. Heating was then stopped, and the temperature was lowered to -40 °C while maintaining the stirring speed.

[0037] 2) The mixed slurry obtained in step 1) is passed through a screw extrusion device (including a screw extruder, melt filter, melt metering pump and film die) at an extrusion temperature of 140 ℃, a twin screw speed of 20 rpm, a metering pump speed of 1 rpm and a melt pressure of 1.0 MPa to obtain polyethylene sheet melt.

[0038] 3) The polyethylene sheet melt obtained in step 2) is first passed through a gaseous medium of nitrogen at 23 °C, and then through a liquid medium of water at 10 °C. The stretching rate in this process is 20 m / min, and the residence time in nitrogen at 23 °C is 1 minute to obtain a polyethylene nascent film.

[0039] 4) The polyethylene nascent film obtained in step 3) is subjected to secondary stretching in an air atmosphere at 20 ℃, at a stretching rate of 0.1 mm / s and a stretching ratio of 128 times, and then heat-set at 125 ℃ for 0.5 hours to obtain polyethylene film S2.

[0040] The thickness and porosity of the polyethylene film S2 obtained in Example 2 were tested. The thickness data is shown in Table 1 and the porosity data is shown in Table 2.

[0041] Example 3 This embodiment illustrates the preparation of polyethylene film using the preparation method of the present invention.

[0042] 1) The molecular weight is 2.50×10 6 Polyethylene (g / mol) and solvent oil with an open flash point of 50 °C were mixed at a concentration of 20 wt% and stirred at 50 °C and 200 rpm for 4 hours to form a slurry. Heating was then stopped, and the temperature was maintained at 50 °C while stirring at the set stirring speed.

[0043] 2) The mixed slurry obtained in step 1) is passed through a screw extrusion device (including a screw extruder, melt filter, melt metering pump and film die) at an extrusion temperature of 320 ℃, a twin screw speed of 300 rpm, a metering pump speed of 20 rpm and a melt pressure of 8.0 MPa to obtain polyethylene sheet melt.

[0044] 3) The polyethylene sheet melt obtained in step 2) is passed through a nitrogen gas medium at -20℃. The stretching rate during this process is 20 m / min, and the residence time in the nitrogen gas at -20℃ is 5 minutes to obtain a polyethylene nascent film.

[0045] 4) The polyethylene nascent film obtained in step 3) is subjected to a second stretching in an air atmosphere at 20 ℃, a stretching rate of 10 mm / s, and a stretching ratio of 2, and then heat-set at 125 ℃ for 24 hours to obtain polyethylene film S3.

[0046] The polyethylene film S3 obtained in Example 3 was tested for thickness and porosity. The thickness data is shown in Table 1 and the porosity data is shown in Table 2.

[0047] Example 4 This embodiment illustrates the preparation of polyethylene film using the preparation method of the present invention.

[0048] 1) The molecular weight is 2.50×10 5Polyethylene (g / mol) and solvent oil with an open flash point of 150 °C were mixed at a concentration of 60 wt% and heated at 115 °C and 60 rpm for 4 hours to form a slurry. Heating was then stopped, and the temperature was cooled to 50 °C while maintaining the set stirring speed.

[0049] 2) The mixed slurry obtained in step 1) is passed through a screw extrusion device (including a screw extruder, melt filter, melt metering pump and film die) at an extrusion temperature of 140 ℃, a twin screw speed of 160 rpm, a metering pump speed of 6 rpm and a melt pressure of 6.0 MPa to obtain polyethylene sheet melt.

[0050] 3) The polyethylene sheet melt obtained in step 2) is first passed through a gaseous medium of helium at -20℃, then through a liquid medium of ethanol at -20℃, and finally through a gaseous medium of nitrogen at -20℃. The stretching rate in this process is 1 m / min, and the residence time in helium and nitrogen at -20℃ is 3 minutes to obtain a polyethylene nascent film.

[0051] 4) The polyethylene nascent film obtained in step 3) is subjected to secondary stretching in an air atmosphere at 105 ℃, a stretching rate of 6 mm / s, and a stretching ratio of 64 times. After heat setting at 90 ℃ for 6 hours, polyethylene film S4 is obtained.

[0052] The polyethylene film S4 obtained in Example 4 was tested for thickness and porosity. The thickness data is shown in Table 1 and the porosity data is shown in Table 2.

[0053] Example 5 This embodiment illustrates the preparation of polyethylene film using the preparation method of the present invention.

[0054] 1) The molecular weight is 3.00×10 6 Polyethylene (g / mol) and o-dichlorobenzene (cuplet flash point 77 °C) were mixed at a concentration of 20 wt% and stirred at 115 °C and 60 rpm for 2 hours to form a slurry. Heating was then stopped, and the temperature was lowered to 23 °C while maintaining the set stirring speed.

[0055] 2) The mixed slurry obtained in step 1) is passed through a screw extrusion device (including a screw extruder, melt filter, melt metering pump and film die) at an extrusion temperature of 140 ℃, a twin screw speed of 20 rpm, a metering pump speed of 6 rpm and a melt pressure of 6.0 MPa to obtain polyethylene sheet melt.

[0056] 3) The polyethylene sheet melt obtained in step 2) is first passed through a gaseous medium of helium at -20℃, then through a liquid medium of ethanol at -20℃, and finally through a gaseous medium of nitrogen at -20℃. The stretching rate in this process is 1 m / min, and the residence time in helium and nitrogen at -20℃ is 5 minutes to obtain a polyethylene nascent film.

[0057] 4) The polyethylene nascent film obtained in step 3) is subjected to secondary stretching in an air atmosphere at 150 ℃, a stretching rate of 3 mm / s, and a stretching ratio of 100 times. After heat setting at 90 ℃ for 1 hour, polyethylene film S5 is obtained.

[0058] The polyethylene film S5 obtained in Example 5 was tested for thickness and porosity. The thickness data is shown in Table 1 and the porosity data is shown in Table 2.

[0059] Comparative Example 1 1) The molecular weight is 1.29×10 6 Polyethylene (g / mol) and decahydronaphthalene (cup flash point 57 °C) were mixed at a concentration of 15 wt% and stirred at 95 °C and 100 rpm for 2 hours to form a slurry. Heating was then stopped, and the temperature was lowered to 23 °C while maintaining the stirring speed.

[0060] 2) The mixed slurry obtained in step 1) is passed through a screw extrusion device (including a screw extruder, melt filter, melt metering pump and film die) at an extrusion temperature of 180 ℃, a twin screw speed of 80 rpm, a metering pump speed of 10 rpm and a melt pressure of 2.5 MPa to obtain polyethylene sheet melt.

[0061] 3) The polyethylene sheet melt obtained in step 2) is first passed through a gaseous medium of air at 23 °C, then through a liquid medium of water at 10 °C, and finally through a gaseous medium of nitrogen at 110 °C. The stretching rate in this process is 0.5 m / min, and the residence time in air at 23 °C and nitrogen at 110 °C is 6 minutes to obtain a polyethylene nascent film.

[0062] 4) The polyethylene nascent film obtained in step 3) is subjected to secondary stretching in an air atmosphere at 110 ℃, at a stretching rate of 0.1 mm / s and a stretching ratio of 64 times, and then heat-set at 60 ℃ for 24 hours to obtain polyethylene film DS1.

[0063] The thickness and porosity of the polyethylene film DS1 obtained in Comparative Example 1 were tested. The thickness data is shown in Table 1, and the porosity data is shown in Table 2.

[0064] Comparative Example 2 1) The molecular weight is 3.00×10 6Polyethylene (g / mol) and o-dichlorobenzene (cuplet flash point 77 °C) were mixed at a concentration of 20 wt% and stirred at 115 °C and 60 rpm for 2 hours to form a slurry. Heating was then stopped, and the temperature was lowered to 23 °C while maintaining the set stirring speed.

[0065] 2) The mixed slurry obtained in step 1) is passed through a screw extrusion device (including a screw extruder, melt filter, melt metering pump and film die) at an extrusion temperature of 140 ℃, a twin screw speed of 20 rpm, a metering pump speed of 6 rpm and a melt pressure of 6.0 MPa to obtain polyethylene sheet melt.

[0066] 3) The polyethylene sheet melt obtained in step 2) is passed through a xenon gas medium at 110 °C. The stretching rate during this process is 0.5 m / min, and the residence time in xenon gas at 110 °C is 9 minutes to obtain a polyethylene primary film.

[0067] 4) The polyethylene nascent film obtained in step 3) is subjected to secondary stretching in an air atmosphere at 100 ℃, at a stretching rate of 0.1 mm / s and a stretching ratio of 64 times, and then heat-set at 60 ℃ for 1 hour to obtain polyethylene film DS2.

[0068] The thickness and porosity of the polyethylene film DS2 obtained in Comparative Example 2 were tested. The thickness data is shown in Table 1, and the porosity data is shown in Table 2.

[0069] Comparative Example 3 A polyethylene film was prepared using the same method as in Example 1, except that in step 1), the solvent opening flash point was 276 °C, denoted as polyethylene film DS3.

[0070] Table 1 Table 2 In Comparative Examples 1 and 2, although solvents with flash points of 50–150 °C and molecular weights of 1 × 10⁻⁶ were used, 5 g / mol~1.0×10 7Using polyethylene in the g / mol range as raw material, but with the residence time of the polyethylene sheet melt in the gaseous medium exceeding 5 minutes, the porosity of the finished film is in the range of 0.1% to 5.0%. In Examples 1 to 5, the residence time of the polyethylene sheet melt in the gaseous medium is less than 5 minutes, and the porosity of the finished film is in the range of 50% to 95%. Among them, in Examples 1 to 2, the residence time is less than 3 minutes, and the porosity of the finished film is in the range of 80% to 95%. In Comparative Example 3, when the flash point of the solvent exceeds 150°C, or when the solvent has poor volatility or is non-volatile, the porosity can only be achieved in the range of 30% to 50%.

[0071] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A process for the production of a polyethylene film, characterized in that, Includes the following steps: 1) Prepare a mixed slurry by mixing a solvent with an open flash point of 50-150 °C and polyethylene resin; then adjust the slurry temperature to the preset temperature range. 2) The mixed slurry obtained in step 1) is extruded through a screw extruder to obtain polyethylene sheet melt; 3) The polyethylene sheet melt obtained in step 2) is initially stretched in a medium environment. By selecting the medium environment and controlling the stretching residence time, the nascent film does not undergo structural collapse and retains the solvent, thus obtaining a nascent polyethylene film. 4) The polyethylene nascent film obtained in step 3) is stretched a second time, and then heat-set to obtain a polyethylene film with the required porosity.

2. The method for preparing polyethylene film according to claim 1, characterized in that, The polyethylene resin mentioned in step 1) has a molecular weight of 1×10⁻⁶. 5 g / mol~1.0×10 7 Within the range of g / mol; the solvent is tetrahydronaphthalene, decahydronaphthalene, solvent oil with an open flash point of 50~150℃, butyl lactate, indene, diethylene glycol butyl ether, tributyl phosphate, o-dichlorobenzene, 2,5-hexanedione, and N-methylpyrrolidone.

3. The method for preparing polyethylene film according to claim 1, characterized in that, The mass concentration of the mixed slurry is 2-60 wt%; the preparation temperature of the mixed slurry is in the range of 50-115 ℃, and the preset temperature range is -40-50 ℃.

4. The method for preparing polyethylene film according to claim 1, characterized in that, The preparation of the mixed slurry is carried out under stirring conditions or under ultrasonic vibration. The stirring conditions include a stirring speed of 60-200 rpm and a stirring preparation time of 0.1-4 hours. The duration of ultrasonic vibration ranges from 0.5 to 120 minutes.

5. The method for preparing polyethylene film according to claim 1, characterized in that, The screw extrusion equipment in step 2) includes a screw extruder, a melt filter, a melt metering pump, and a film die; the screw temperature of the screw extruder is in the range of 140 to 320 ℃, the screw speed is in the range of 20 to 300 rpm, the melt pressure is in the range of 1 to 8 MPa, and the speed of the melt metering pump is in the range of 1 to 20 rpm.

6. The method for preparing polyethylene film according to claim 1, characterized in that, The medium temperature mentioned in step 3) is -20 to 110 ℃; the initial stretching ratio is 1 to 20 times, the initial stretching speed is 0.1 to 20 m / min; and the thickness of the polyethylene nascent film is 1 to 2500 μm.

7. The method for preparing polyethylene film according to claim 1, characterized in that, In step 3), the medium used in the drawing process shall be selected from one of the following medium types: a. The stretching process involves only a gaseous medium; b. The stretching process involves only a liquid medium; c. The stretching process first passes through a gaseous medium and then through a liquid medium; d. The stretching process first passes through a liquid medium, then a gaseous medium, and then back to a liquid medium; e. The stretching process first passes through a gaseous medium, then a liquid medium, and then back through a gaseous medium; Furthermore, in any medium, the total stretching residence time of the polyethylene sheet melt in the gaseous medium is controlled to be less than 5 minutes.

8. The method for preparing polyethylene film according to claim 7, characterized in that, In any of the above media formats, the total stretching residence time of the polyethylene sheet melt in the gaseous medium is controlled to be less than 3 minutes.

9. The method of producing a polyethylene film according to any one of claims 1 to 8, characterized in that, The liquid medium is one or more of water, anhydrous ethanol, n-hexane, n-heptane, dichloromethane, n-pentane, petroleum ether, diethylamine, and hexadiene, and the gaseous medium is one or more of air, carbon dioxide, nitrogen, helium, neon, argon, krypton, and xenon.

10. The method for preparing polyethylene film according to claim 1, characterized in that, The secondary stretching temperature in step 4) is in the range of 20 to 150 ℃, the secondary stretching speed is in the range of 0.1 to 10 mm / s, and the stretching ratio is in the range of 2 to 576 times; the heat setting temperature is 60 to 125 ℃, and the setting time is 0.5 to 24 hours.

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