Insulating film, preparation method and application in power battery

Abstract

The invention relates to the technical field of insulating films, and discloses an insulating film, a preparation method and an application in a power battery, specifically, iminodiacetic acid, 10-undecylene-1-ol, 3, 5-di-tert-butyl-4-hydroxybenzyl alcohol and 2-chloroethyl sodium sulfonate are used as raw materials based on an esterification reaction and substitution reaction mechanism, and the insulating film is prepared through a one-step reaction. The alkenylation hindered phenol type sodium sulfonate monomer is prepared; the preparation method comprises the following steps: compounding an alkenylation hindered phenol type sodium sulfonate monomer and quaternary ammonium salt type PA6 resin through an electrostatic adsorption effect to prepare alkenylation hindered phenol type PA6 resin; the preparation method comprises the following steps: under the action of a molten state and a free radical initiator, grafting alkenyl hindered phenol type PA6 resin to a main chain of LLDPE (Linear Low Density Polyethylene) resin to prepare a functional master batch; and introducing the functionalized master batch into an eleven-layer co-extrusion film, and preparing the insulating film by adopting an eleven-layer co-extrusion blow molding film forming process. The insulating film prepared by the invention has excellent insulating property and mechanical property.

Description

Technical Field

[0001] This invention relates to the field of insulating film technology, and more particularly to an insulating film, its preparation method, and its application in power batteries. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the safety, reliability, and lifespan of power batteries, as the core power source, have received high attention from the industry. Battery packaging is a key step in power battery manufacturing. It not only needs to achieve physical protection and sealing of the battery cells, but also needs to block conductive paths through insulation design to avoid short circuit risks caused by accidental contact between the battery cells and external structures or between battery cells. Therefore, insulating films have become key materials, and their performance directly affects the safety level and long-term operational stability of power batteries.

[0003] The preferred materials for insulating films are polyolefins such as polyethylene (PE) and polypropylene (PP). However, these films have poor heat resistance (long-term operating temperature below 100℃) and are prone to thermal shrinkage or even melting under the high-temperature conditions of batteries, leading to insulation failure. In contrast, polyamide (PA) has a higher thermal decomposition temperature and excellent mechanical properties, making it an ideal insulating material. Therefore, in the design of insulating films, polyamide / polyethylene multilayer co-extruded composite films are used to achieve excellent insulation performance.

[0004] However, under high-temperature melting conditions, polyethylene undergoes oxidative cross-linking, which leads to a decrease in the insulation and mechanical properties of the polyamide / polyethylene multilayer co-extruded composite film.

[0005] Studies have found that hindered phenolic antioxidants can not only inhibit the thermal oxidation and degradation of polyethylene resin during extrusion, but also effectively capture free radicals to inhibit cross-linking reactions, thereby improving the processing performance of polyethylene melt. Summary of the Invention

[0006] Based on molecular design principles, this invention independently developed an alkenylated hindered phenolic sodium sulfonate monomer. This monomer was compounded with quaternary ammonium salt PA6 resin through electrostatic adsorption to obtain alkenylated hindered phenolic PA6 resin. Subsequently, it was grafted onto the LLDPE resin backbone through a free radical addition reaction to obtain a functionalized masterbatch. Finally, an insulating film was obtained through an eleven-layer co-extrusion blow molding process. This film exhibits excellent insulation and mechanical properties.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing an insulating film includes the following steps:

[0009] Step 1: Synthesize the alkenylation hindered phenolic sulfonate sodium monomer;

[0010] Step 2: The alkenylated hindered phenolic sodium sulfonate monomer is compounded with quaternary ammonium salt PA6 resin by electrostatic adsorption to obtain alkenylated hindered phenolic PA6 resin.

[0011] Quaternary ammonium salt type PA6 resin is prepared by modifying PA6 resin with 2,3-epoxypropyltrimethylammonium chloride;

[0012] Step 3: Under the action of molten state and free radical initiator, the alkenylated hindered phenolic PA6 resin is grafted onto the LLDPE resin backbone to obtain functionalized masterbatch;

[0013] The membrane structure, formulation and dosage of each layer of the eleven-layer co-extruded film were designed. Functionalized masterbatch was introduced into the eleven-layer co-extruded film. The insulating film was produced by using the eleven-layer co-extruded blow molding process.

[0014] Preferably, the method for preparing the alkenylation hindered phenolic sulfonate sodium monomer is as follows:

[0015] Intermediate a was prepared by esterification of the carboxyl group in 1 molar equivalent of iminodiacetic acid with the hydroxyl group in 1 molar equivalent of 10-undecen-1-ol;

[0016] Based on the esterification reaction mechanism, intermediate a reacts with 3,5-di-tert-butyl-4-hydroxybenzyl alcohol in a molar ratio of 1:0.99-1 to obtain intermediate b.

[0017] The alkenylated hindered phenolic sulfonate monomer was prepared by a substitution reaction between the imino group in 1 molar equivalent intermediate b and the chlorine functional group in 1 molar equivalent of sodium 2-chloroethyl sulfonate.

[0018] Preferably, the preparation method of the quaternary ammonium salt type PA6 resin is as follows: PA6 resin and 2,3-epoxypropyltrimethylammonium chloride are mixed evenly and then placed in a twin-screw extruder for melt reaction extrusion granulation. The melt temperature is 200-220℃ to obtain the quaternary ammonium salt type PA6 resin.

[0019] Preferably, the membrane structure, formulation, and dosage of the eleven-layer co-extruded membrane are as follows:

[0020] First layer: The formula is 100wt% functionalized masterbatch, and the dosage is 10-20 parts by weight;

[0021] Second layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight;

[0022] The third layer consists of 40-60 wt% LDPE resin and 40-60 wt% LLDPE resin, with a dosage of 5-10 parts by weight.

[0023] Fourth layer: The formula consists of 40-60wt% LDPE resin and 40-60wt% LLDPE resin, with a dosage of 5-10 parts by weight;

[0024] Fifth layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight;

[0025] Sixth layer: The formula is 100wt% PA6 resin, and the dosage is 4-8 parts by weight;

[0026] Seventh layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight;

[0027] Eighth layer: The formula consists of 40-60wt% LDPE resin and 40-60wt% LLDPE resin, and the dosage is 5-10 parts by weight;

[0028] Ninth layer: The formula consists of 40-60wt% LDPE resin and 40-60wt% LLDPE resin, and the dosage is 5-10 parts by weight;

[0029] Tenth layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight;

[0030] Eleventh layer: The formula is 100wt% functionalized masterbatch I, and the dosage is 10-20 parts by weight.

[0031] Preferably, the process parameters of the screw extruders corresponding to the first and eleventh layers are set as follows: the temperatures of zones 1-4 are 230-250℃, 240-260℃, 250-270℃, and 260-280℃, and the screw speed is 25-35 r / min;

[0032] The process parameters for the screw extruders corresponding to the second, fifth, seventh, and tenth layers are set as follows: the temperatures in zones 1-4 are 120-130℃, 140-160℃, 160-170℃, and 155-165℃, respectively, and the screw speed is 10-20 r / min.

[0033] The process parameters for the screw extruder corresponding to the sixth layer are set as follows: zone 1-4 temperatures are 220-240℃, 230-250℃, 240-260℃, and 250-270℃, and the screw speed is 35-45 r / min.

[0034] The process parameters for the screw extruders corresponding to the third, fourth, sixth, eighth, and ninth layers are set as follows: temperatures in zones 1-4 are 170-180℃, 180-190℃, 190-200℃, and 195-205℃, respectively, and the screw speed is 30-40 r / min.

[0035] Preferably, the thickness of the insulating film is 40-60 μm.

[0036] Preferably, the graphene oxide has an average thickness of 4 nm and a diameter ranging from 3 to 10 μm.

[0037] Preferably, the free radical initiator is one of dicumyl peroxide and tert-butyl peroxide.

[0038] Preferably, the functionalized masterbatch is formulated as follows: 75-85 wt% alkenylated hindered phenolic PA6 resin and 15-25 wt% LLDPE resin.

[0039] The formulation of the alkenylated hindered phenolic PA6 resin is as follows: 80-120 parts by weight of quaternary ammonium salt PA6 resin, 6-10 parts by weight of alkenylated hindered phenolic sodium sulfonate monomer, and 80-120 parts by weight of deionized water.

[0040] Preferably, the insulating film is used for power battery encapsulation.

[0041] The beneficial effects of this invention are as follows:

[0042] Based on the esterification and substitution reaction mechanisms, an alkenylation hindered phenolic sodium sulfonate monomer was prepared using iminodiacetic acid, 10-undecen-1-ol, 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and sodium 2-chloroethyl sulfonate as raw materials.

[0043] Based on the epoxy ring-opening reaction mechanism, 2,3-epoxypropyltrimethylammonium chloride was grafted onto the end of the PA6 resin molecular chain to prepare quaternary ammonium salt type PA6 resin.

[0044] The alkenylated hindered phenolic sodium sulfonate monomer was compounded with quaternary ammonium salt PA6 resin by electrostatic adsorption to obtain alkenylated hindered phenolic PA6 resin.

[0045] Functionalized masterbatch was prepared by melt grafting LLDPE resin with alkenylated hindered phenolic PA6 resin under the action of free radical initiator.

[0046] Functionalized masterbatch is introduced into an eleven-layer co-extruded film, and an insulating film is produced by using an eleven-layer co-extruded blow molding process.

[0047] Experimental results demonstrate that the insulating film prepared by this invention possesses excellent insulation and mechanical properties. Detailed Implementation

[0048] Example 1:

[0049] The preparation of alkenylation-hindered phenolic sulfonate sodium monomers includes the following steps:

[0050] Step S1: Preparation of intermediate a. The preparation mechanism is as follows: intermediate a is obtained through esterification reaction between the carboxyl group in iminodiacetic acid and the hydroxyl group in 10-undecen-1-ol. The specific experimental steps are as follows: 2.67 g of iminodiacetic acid and 3.41 g of 10-undecen-1-ol are added to 50 mL of N,N-dimethylformamide and stirred evenly. Then, 0.08 g of p-toluenesulfonic acid is added. After the addition is complete, heating is started and the temperature is controlled at 110 °C. The reaction is stirred for 8 h under nitrogen protection. After the reaction is completed, the solvent is removed by vacuum distillation, washed, and dried under vacuum at 40 °C for 12 h to obtain intermediate a. Its chemical structural formula is:

[0051] ;

[0052] Step S2: Preparation of intermediate b. The preparation mechanism is as follows: intermediate b is obtained by esterification reaction between the carboxyl group in intermediate a and the hydroxyl group in 3,5-di-tert-butyl-4-hydroxybenzyl alcohol. The specific experimental steps are as follows: 2.9 g of intermediate a, 2.4 g of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol, and 40 mL of N,N-dimethylformamide are added to a 250 mL three-necked flask and mechanically stirred until homogeneous. 0.06 g of p-toluenesulfonic acid is added, and the system temperature is raised to 110 °C and reacted at this temperature for 8 h. After the reaction is complete, N,N-dimethylformamide is removed by vacuum distillation, and the mixture is dried in a vacuum drying oven at 40 °C for 10 h to obtain intermediate b. Its chemical structural formula is:

[0053] ;

[0054] Step S3: Preparation of alkenylated hindered phenolic sodium sulfonate monomer. The preparation mechanism is as follows: the alkenylated hindered phenolic sodium sulfonate monomer is obtained by the substitution reaction between the imino group in intermediate b and the chlorine functional group in sodium 2-chloroethyl sulfonate. The specific experimental steps are as follows: 5.1 g of intermediate b and 50 mL of anhydrous ethanol are added to a 250 mL three-necked flask equipped with a thermometer, stirrer, and reflux condenser. The mixture is mechanically stirred until homogeneous. Then, 1.7 g of sodium 2-chloroethyl sulfonate and 1.2 g of sodium carbonate are added. The mixture is stirred and refluxed at 80 °C for 3 h. After the reaction is complete, the mixture is filtered, washed, and vacuum dried at 50 °C for 8 h to obtain the alkenylated hindered phenolic sodium sulfonate monomer. Its chemical structural formula is:

[0055] ;

[0056] The 1H NMR characterization of the alkenylation-hindered phenolic sulfonate sodium monomer is as follows:

[0057] 1H NMR (DMSO-d6, 400MHz) δ: 1.27-1.41 (m, 12H), 1.45 (s, 18H), 1.60-1.66 (m, 2H), 2.01-2.05 (m, 2H), 2.90-2.97 (m, 4H), 3.54-3.57(d, 4H), 4.07-4.09(t, 2H), 4.96-5.11(dd, 2H), 5.16(s, 2H), 5.68(s, 1H), 5.73-5.80(m, 1H), 7.13(s, 2H).

[0058] Example 2:

[0059] Quaternary ammonium salt type PA6 resin comprises the following raw materials in parts by weight:

[0060] 100 parts of PA6 resin (model F136 / NA99001 / 4229D);

[0061] 2 parts of 2,3-epoxypropyltrimethylammonium chloride;

[0062] The preparation method of quaternary ammonium salt type PA6 resin is as follows: PA6 resin and 2,3-epoxypropyltrimethylammonium chloride are mixed evenly in a high-speed mixer, and then placed in a twin-screw extruder for melt reaction extrusion at a melting temperature of 210℃. After that, it is placed in a 50℃ forced-air oven for drying for 10 hours to obtain quaternary ammonium salt type PA6 resin.

[0063] Example 3:

[0064] The olefinically hindered phenolic PA6 resin comprises the following raw materials in parts by weight:

[0065] 100 parts of quaternary ammonium salt type PA6 resin;

[0066] 8 parts of alkenylation hindered phenolic sulfonate sodium monomer

[0067] 100 portions of deionized water;

[0068] The preparation method of alkenylated hindered phenolic PA6 resin includes the following steps: adding quaternary ammonium salt PA6 resin to deionized water, ultrasonically dispersing for 30 min, adding alkenylated hindered phenolic sodium sulfonate monomer, stirring at 300 r / min for 3 h, filtering after standing, and vacuum drying at 40℃ for 12 h to obtain alkenylated hindered phenolic PA6 resin.

[0069] Example 4:

[0070] (1) Prepare functionalized masterbatch I, the raw material formula is: 80wt% alkenylated hindered phenolic PA6 resin and 20wt% LLDPE resin (model DFDA 7047);

[0071] In the preparation of functionalized masterbatch I via melt grafting, dicumyl peroxide was used as the initiator, and the amount of dicumyl peroxide was 0.1 wt% of the LLDPE resin.

[0072] The preparation method of functionalized masterbatch I is as follows: LLDPE resin, alkenylated hindered phenolic PA6 resin and dicumyl peroxide are added to a high-speed mixer and stirred evenly. Then, the mixture is placed in a twin-screw extruder for melt extrusion granulation. The screw speed of the twin-screw extruder is 150 r / min, the temperature of zone 1 is 230℃, the temperature of zone 2 is 245℃, the temperature of zone 3 is 260℃, and the temperature of zone 4 is 265℃, thus obtaining functionalized masterbatch I.

[0073] (2) Functionalized Masterbatch II, the raw material formula is: 85wt% alkenylated hindered phenolic PA6 resin and 15wt% LLDPE resin;

[0074] The only difference between the preparation process of functionalized masterbatch II and that of functionalized masterbatch I is that the raw material formulation of functionalized masterbatch II is used instead of that of functionalized masterbatch I.

[0075] (3) Functionalized Masterbatch III, the raw material formula is: 75wt% alkenylated hindered phenolic PA6 resin and 25wt% LLDPE resin;

[0076] The only difference between the preparation process of functionalized masterbatch III and that of functionalized masterbatch I is that the raw material formulation of functionalized masterbatch III is used instead of that of functionalized masterbatch I.

[0077] Example 5:

[0078] (1) Preparation of insulating film I, including the following steps:

[0079] Step 1: Set the insulating film I as an eleven-layer film structure. The formulation and dosage of each layer are as follows:

[0080] First layer: The formula is 100wt% functionalized masterbatch I, and the dosage is 15 parts by weight;

[0081] Second layer: The formula is 100 wt% PE-g-MAH resin, and the amount used is 8 parts by weight;

[0082] The third layer consists of 50 wt% LDPE resin and 50 wt% LLDPE resin, with a dosage of 8 parts by weight.

[0083] Fourth layer: The formula consists of 50wt% LDPE resin and 50wt% LLDPE resin, with a dosage of 8 parts by weight.

[0084] Fifth layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 8 parts by weight;

[0085] Sixth layer: The formula is 100wt% PA6 resin, and the dosage is 6 parts by weight;

[0086] Seventh layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 8 parts by weight;

[0087] Eighth layer: The formula consists of 50wt% LDPE resin and 50wt% LLDPE resin, with a dosage of 8 parts by weight.

[0088] Ninth layer: The formula consists of 50wt% LDPE resin and 50wt% LLDPE resin, with a dosage of 8 parts by weight;

[0089] The tenth layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 8 parts by weight;

[0090] Eleventh layer: The formula is 100wt% functionalized masterbatch I, and the dosage is 15 parts by weight;

[0091] Step 2: The raw materials of each film layer in Step 1 are respectively fed into the hoppers of the eleven screw extruders of the eleven-layer co-extrusion film blow molding unit. After stirring and mixing, the molten resin is gathered at the die head through the distributor, and then extruded through the die head for blow molding, cooling and winding to prepare an insulating film I with a thickness of 45μm.

[0092] The process parameters for the screw extruders corresponding to the first and eleventh layers are set as follows: temperatures in zones 1-4 are 240℃, 250℃, 260℃, and 270℃, and the screw speed is 30 r / min.

[0093] The process parameters for the screw extruders corresponding to the second, fifth, seventh, and tenth layers are set as follows: the temperatures in zones 1-4 are 125℃, 150℃, 165℃, and 160℃, and the screw speed is 15 r / min.

[0094] The process parameters for the screw extruder corresponding to the sixth layer are set as follows: temperatures in zones 1-4 are 230℃, 240℃, 250℃, and 260℃, and the screw speed is 40 r / min.

[0095] The process parameters for the screw extruders corresponding to the third, fourth, sixth, eighth, and ninth layers are set as follows: temperatures in zones 1-4 are 175℃, 185℃, 195℃, and 200℃, and the screw speed is 35 r / min.

[0096] Among them, the LLDPE resin is designated as DFDA 7047; the LDPE resin is designated as 2426H; the PE-g-MAH resin is designated as 4288; and the PA6 resin is designated as F136 / NA99001 / 4229D.

[0097] (2) Prepare insulating film II, which differs from insulating film I only in that functionalized masterbatch I is replaced by functionalized masterbatch II.

[0098] (3) Prepare insulating film III, which differs from insulating film I only in that functionalized masterbatch I is replaced by functionalized masterbatch III.

[0099] Performance testing:

[0100] I. Mechanical Properties: According to GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets", the tensile strength and elongation at break of the insulating film samples were tested using a universal testing machine. The length of the insulating film sample was 200 mm and the width was 20 mm. The tensile speed was 500 mm / min.

[0101] II. Insulation Resistance: The insulation resistance of the insulating film sample was tested according to GB / T 31838.4-2019 "Dielectric and Resistive Properties of Solid Insulating Materials - Part 4: Resistive Properties (DC Method) - Insulation Resistance".

[0102] The test results are shown in Table 1 below;

[0103] Table 1 Performance test results of insulating films

[0104] Product Number Longitudinal tensile strength (MPa) Longitudinal elongation at break (%) Insulation resistance (Ω) Insulating film I 46.5 387 <![CDATA[3.13×10 12 ]]> Insulating film II 48.1 365 <![CDATA[1.57×10 12 ]]> Insulating film III 42.9 401 <![CDATA[4.94×10 12 ]]> Comparative Example 35.3 312 <![CDATA[5.16×10 8 ]]>

[0105] Comparative example: The raw material formulations for the first and eleventh layers are: 80wt% PA6 resin (model F136 / NA99001 / 4229D) and 20wt% LLDPE resin, with a dosage of 15 parts by weight;

[0106] The only difference between the preparation process of the comparative example and the preparation process of functionalized masterbatch I is that the first and eleventh layer raw material formulations in the comparative example are used instead of the first and eleventh layer raw material formulations in functionalized masterbatch I.

[0107] As can be seen from the experimental results in Table 1, the insulating film prepared by this invention has achieved significant improvements in both mechanical and insulating properties, which are beneficial technical effects.

Claims

1. A method for preparing an insulating film, characterized in that, Includes the following steps: Step 1: Synthesize the alkenylation hindered phenolic sulfonate sodium monomer, whose chemical structural formula is: ； Step 2: The alkenylated hindered phenolic sodium sulfonate monomer is compounded with quaternary ammonium salt PA6 resin by electrostatic adsorption to obtain alkenylated hindered phenolic PA6 resin. Quaternary ammonium salt type PA6 resin is prepared by modifying PA6 resin with 2,3-epoxypropyltrimethylammonium chloride; Step 3: Under the action of molten state and free radical initiator, the alkenylated hindered phenolic PA6 resin is grafted onto the LLDPE resin backbone to obtain functionalized masterbatch; The membrane structure, formulation and dosage of each layer of the eleven-layer co-extruded film were designed. Functionalized masterbatch was introduced into the eleven-layer co-extruded film. The insulating film was produced by using the eleven-layer co-extruded blow molding process.

2. The method for preparing an insulating film according to claim 1, characterized in that, The method for preparing the alkenylated hindered phenolic sulfonate sodium monomer is as follows: Intermediate a was prepared by esterification of the carboxyl group in 1 molar equivalent of iminodiacetic acid with the hydroxyl group in 1 molar equivalent of 10-undecen-1-ol; Based on the esterification reaction mechanism, intermediate a reacts with 3,5-di-tert-butyl-4-hydroxybenzyl alcohol in a molar ratio of 1:0.99-1 to obtain intermediate b; The alkenylated hindered phenolic sulfonate monomer was prepared by a substitution reaction between the imino group in 1 molar equivalent intermediate b and the chlorine functional group in 1 molar equivalent of sodium 2-chloroethyl sulfonate.

3. The method for preparing an insulating film according to claim 1, characterized in that, The preparation method of the quaternary ammonium salt type PA6 resin is as follows: PA6 resin and 2,3-epoxypropyltrimethylammonium chloride are mixed evenly and then placed in a twin-screw extruder for melt reaction extrusion. The melt temperature is 200-220℃ to obtain the quaternary ammonium salt type PA6 resin.

4. The method for preparing an insulating film according to claim 1, characterized in that, The membrane structure, formulation, and dosage of the eleven-layer co-extruded membrane are as follows: First layer: The formula is 100wt% functionalized masterbatch, and the dosage is 10-20 parts by weight; Second layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight; The third layer consists of 40-60 wt% LDPE resin and 40-60 wt% LLDPE resin, with a dosage of 5-10 parts by weight. Fourth layer: The formula consists of 40-60wt% LDPE resin and 40-60wt% LLDPE resin, with a dosage of 5-10 parts by weight; Fifth layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight; Sixth layer: The formula is 100wt% PA6 resin, and the dosage is 4-8 parts by weight; Seventh layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight; Eighth layer: The formula consists of 40-60wt% LDPE resin and 40-60wt% LLDPE resin, and the dosage is 5-10 parts by weight; Ninth layer: The formula consists of 40-60wt% LDPE resin and 40-60wt% LLDPE resin, and the dosage is 5-10 parts by weight; Tenth layer: The formula is 100 wt% PE-g-MAH resin, and the dosage is 5-10 parts by weight; Eleventh layer: The formula is 100wt% functionalized masterbatch I, and the dosage is 10-20 parts by weight.

5. The method for preparing an insulating film according to claim 4, characterized in that, The process parameters for the screw extruders corresponding to the first and eleventh layers are set as follows: the temperatures in zones 1-4 are 230-250℃, 240-260℃, 250-270℃, and 260-280℃, and the screw speed is 25-35 r / min. The process parameters for the screw extruders corresponding to the second, fifth, seventh, and tenth layers are set as follows: the temperatures in zones 1-4 are 120-130℃, 140-160℃, 160-170℃, and 155-165℃, respectively, and the screw speed is 10-20 r / min. The process parameters for the screw extruder corresponding to the sixth layer are set as follows: zone 1-4 temperatures are 220-240℃, 230-250℃, 240-260℃, and 250-270℃, and the screw speed is 35-45 r / min. The process parameters for the screw extruders corresponding to the third, fourth, sixth, eighth, and ninth layers are set as follows: temperatures in zones 1-4 are 170-180℃, 180-190℃, 190-200℃, and 195-205℃, respectively, and the screw speed is 30-40 r / min.

6. An insulating film prepared according to any one of claims 1-5, characterized in that, The thickness of the insulating film is 40-60 μm.

7. An insulating film according to claim 6, characterized in that, The graphene oxide has an average thickness of 4 nm and a diameter ranging from 3 to 10 μm.

8. An insulating film according to claim 6, characterized in that, The free radical initiator is one of dicumyl peroxide and tert-butyl peroxide.

9. An insulating film according to claim 6, characterized in that, The formulation of the functionalized masterbatch is: 75-85 wt% alkenylated hindered phenolic PA6 resin and 15-25 wt% LLDPE resin. The formulation of the alkenylated hindered phenolic PA6 resin is as follows: 80-120 parts by weight of quaternary ammonium salt PA6 resin, 6-10 parts by weight of alkenylated hindered phenolic sodium sulfonate monomer, and 80-120 parts by weight of deionized water.

10. An insulating film according to claim 6, characterized in that, The insulating film is used for power battery encapsulation.

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