Preparation method of high-tensile PET (polyethylene terephthalate) flame-retardant film for insulation and fire prevention of battery module

Abstract

The invention relates to the technical field of high polymer material processing, in particular to a preparation method of an insulating and fireproof high-tensile PET (polyethylene terephthalate) flame-retardant film for a battery module, which comprises the following steps: S1, weighing all components according to a preset proportion, and uniformly mixing to form a premixed modified material; s2, carrying out melt copolymerization reaction on the premixed modified material to form a modified PET copolymer; s3, the modified PET copolymer is melted and then subjected to tape casting processing, and a primary membrane material is prepared; s4, carrying out tension heating pretreatment; s5, carrying out synchronous longitudinal and transverse stretching treatment to obtain a high-strength flame-retardant film; s6, carrying out heat setting treatment; s7, the surface is coated with an electric insulation coating; and S8, static elimination and constant-tension rolling are conducted, and a finished product is obtained. According to the invention, the PET film with high tensile strength, dimensional stability and flame-retardant and insulating properties is prepared through synergistic modification and integrated processing technologies, and the defects of existing materials in the aspects of thermal stability and function coordination are overcome.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, and in particular to a method for preparing a high tensile strength PET flame-retardant film for insulation and fire protection of battery modules. Background Technology

[0002] With the development of new energy power battery systems, energy storage modules, and consumer electronics, higher requirements have been placed on the safety, reliability, and environmental adaptability of materials inside battery modules. Among them, polyethylene terephthalate (PET) film, used as a cell spacer or structural covering material, has gradually become a core material in the insulation and protection structure of battery modules due to its certain mechanical strength and thermal stability. However, under complex operating environments such as high heat, high pressure, and external impact, conventional PET film is prone to dimensional shrinkage, melt perforation, or electrical breakdown, and cannot simultaneously meet the comprehensive requirements of electrical insulation, thermal flame retardancy, and high tensile strength.

[0003] Existing technologies typically suffer from the following problems: First, additive flame retardants are prone to migration or precipitation during subsequent thermal processing, leading to unstable flame retardant performance; second, multilayer composite structures increase process complexity, hindering large-scale continuous production; third, while some modification methods enhance flame retardancy, they sacrifice the film's mechanical tensile strength and flexibility, affecting winding processing and long-term service performance. Therefore, there is an urgent need for a method to prepare a high-tensile-strength PET flame-retardant film for battery module insulation and fire protection to address these issues. Summary of the Invention

[0004] To achieve the above objectives, the present invention provides a method for preparing a high tensile strength PET flame-retardant film for insulation and fire protection of battery modules.

[0005] A method for preparing a high tensile strength PET flame-retardant film for insulation and fire protection of battery modules includes the following steps: S1: Weigh out ethylene glycol phthalate chips, phosphorus-based reactive flame retardant, nanofiller and chain extender according to the preset ratio, and mix them evenly to form a premixed modified material; S2: The premixed modified material undergoes a melt copolymerization reaction to form a modified PET copolymer; S3: The modified PET copolymer is melted and then cast to obtain a primary film material; S4: Perform tension heating pretreatment on the primary membrane material in both the transverse and longitudinal directions; S5: Simultaneous longitudinal and transverse stretching of the preheated membrane material to obtain a high-strength flame-retardant membrane. S6: The high-strength flame-retardant film is heat-set to stabilize its dimensions; S7: After heat setting, an electrically insulating coating is applied to the surface of the flame-retardant film, and the coating adhesion is enhanced by corona discharge treatment. S8: The flame-retardant film with completed surface treatment is subjected to static elimination and constant tension winding to obtain a high tensile strength PET flame-retardant film product for battery module insulation and fire protection.

[0006] Optionally, the ethylene glycol phthalate chips, phosphorus-based reactive flame retardant, nanofiller, and chain extender are respectively expressed in the following mass percentages: 88-95.5% ethylene glycol phthalate slices; Phosphorus-based reactive flame retardants: 3-7%; Nanofiller 1-3%; Chain extender 0.5-2%; The nanofiller is selected from nano-alumina or nano-montmorillonite; the chain extender is selected from PBT glycol-type chain extender or adipic acid-based chain extender.

[0007] Optionally, S1 specifically includes: S11: Weigh out ethylene glycol phthalate chips, phosphorus-based reactive flame retardant, nanofiller and chain extender by mass percentage, and place them in a mixer at room temperature; S12: Set the mixer speed to 800-1200 rpm, turn on the stirring function, and continue mixing for 5-10 minutes, during which the material temperature is maintained at 40-50℃; S13: Transfer the stirred material into a vacuum drying oven and dry it at 115-125℃ for 4-6 hours to remove adsorbed moisture and volatiles from the surface of the material and obtain a uniformly dried premixed modified material.

[0008] Optionally, S2 specifically includes: S21: The premixed modified material is fed into a twin-screw reactive extruder, the temperature of each section of the extruder is set to 240℃~280℃, and a vacuum of -0.08~-0.095MPa is applied to remove oligomers and volatiles; S22: Control the main screw speed of the extruder at 60-120 rpm to allow the material to melt and fully mix under the shearing of the screw, so that the phosphorus flame retardant and PET molecular chain can undergo a copolymerization reaction. S23: The material after copolymerization reaction is completed is extruded from the die head, cooled and solidified by a cooling water bath at a temperature controlled between 15℃ and 30℃, and then obtained as modified PET copolymer particles with a particle size of 2 to 4 mm by a pelletizing mechanism.

[0009] Optionally, S3 specifically includes: S31: Add the modified PET copolymer particles into a single-screw extruder, set the extrusion temperature to 250℃~270℃, and the screw speed to 40~80 rpm, so that they melt to form a uniform melt; S32: The molten material is extruded onto the casting roller through a wide T-shaped die, with the die temperature controlled at 255℃~275℃ and the surface temperature of the casting roller controlled at 15℃~25℃; S33: Adjust the winding speed to 6-12 meters / minute, and wind the cooled and formed membrane material under constant tension to obtain a primary membrane material with a thickness of 15-25 micrometers.

[0010] Optionally, S4 specifically includes: S41: Pass the primary membrane material through the longitudinal tension heating roller group in sequence. Set the roller surface temperature to 70℃~90℃, control the membrane tension to 5~15N, and maintain the membrane material running speed at 10~20 meters / minute so that it completes the tension heating treatment in the longitudinal direction. S42: The longitudinally processed membrane material is introduced into the transverse preheating box. The temperature of the box is controlled at 70℃~95℃, the transmission path is set to 3~6 meters, and the transverse tension is controlled at 4~10N by a tension traction device to complete the transverse tension heating treatment and obtain the pre-stretched membrane material with bidirectional prestress.

[0011] Optionally, S5 specifically includes: S51: Before stretching, the membrane material is introduced into the synchronous biaxial stretching device, and the temperature of the membrane material is first raised to 90℃~110℃ in the preheating zone. S52: Apply longitudinal and transverse tensile forces to the membrane material simultaneously in the stretching zone. The longitudinal stretching ratio is set to 3.0 to 3.5 times, the transverse stretching ratio is set to 3.0 to 3.3 times, and the stretching rate is controlled to be 50 to 80 meters per minute. S53: The stretched membrane material is introduced into the cooling zone through a fixed-width guide rail to rapidly reduce the membrane temperature to 40℃~60℃, thereby obtaining a high-strength flame-retardant membrane with a thickness of 8~15 micrometers.

[0012] Optionally, S6 specifically includes: S61: Introduce the high-strength flame-retardant film into the heat setting device, use an infrared heater to heat the film material in a non-contact manner, and set the setting temperature to 180℃~210℃. S62: Set a constant tension of 5-12N in the shaping zone and control the membrane material conveying speed to 10-20 meters / minute; S63: The continuous heating treatment time is controlled at 3 to 6 seconds. After the membrane material is output from the shaping area, it is introduced into the slow cooling section. The slow cooling temperature is set to 60℃ to 80℃ to complete the dimensional stabilization treatment of the high-strength flame-retardant membrane.

[0013] Optionally, S7 specifically includes: S71: The heat-set high-strength flame-retardant film is conveyed to the coating station, and an electrically insulating coating is uniformly applied to one side of the film material by roller coating. The dry film thickness after coating is 0.5 to 1.0 micrometers. S72: Introduce the coated film into a hot air drying oven, set the drying temperature to 80℃~120℃, and the drying time to 3~6 minutes to complete the coating curing; S73: Perform corona discharge treatment on the dried membrane material. The treatment voltage is set to 6-12kV and the treatment speed is 10-20 m / min, so that the corona energy density on the membrane surface reaches 0.8-1.5W·min / m².

[0014] Optionally, S8 specifically includes: S81: The flame-retardant film with completed surface treatment is introduced into the electrostatic elimination device. The surface of the film is treated with AC high-voltage ion bars. The working voltage is set to 6-10kV and the action distance is controlled at 5-15cm to neutralize the accumulated charge on the surface of the film. S82: The flame-retardant film after static elimination is introduced into the winding station. The winding tension is set to 5-12N by the constant tension control system, and the winding speed is set to 8-15 meters / minute to complete the winding and collection of the flame-retardant film.

[0015] The beneficial effects of this invention are: This invention constructs a polyethylene terephthalate system synergistically modified with phosphorus-based reactive flame retardants, nanofillers, and chain extenders. Combined with continuous processes such as melt copolymerization, biaxial stretching, heat setting, and electrical insulation coating, it achieves stable embedding of flame retardant components in the molecular structure, effectively avoiding the problems of flame retardant migration and precipitation.

[0016] This invention ensures the dimensional stability and structural integrity of the film under high-temperature conditions by simultaneously controlling the orientation structure and thermal stability of the film material.

[0017] This invention improves the electrical insulation performance and interfacial adhesion of the film material by employing a synergistic treatment of surface coating and corona polarization, thereby enhancing its adaptability to complex internal structures of battery modules. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the method for preparing high tensile strength PET flame retardant film according to an embodiment of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0021] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.

[0022] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.

[0023] Example 1 like Figure 1 As shown, a method for preparing a high tensile strength PET flame-retardant film for insulation and fire protection of battery modules includes the following steps: S1: Weigh out ethylene phthalate (PET) chips, phosphorus-based reactive flame retardant, nanofiller and chain extender according to the preset ratio, and mix them evenly to form a premixed modified material; S2: The premixed modified material undergoes a melt copolymerization reaction to form a modified PET copolymer; S3: The modified PET copolymer is melted and then cast to obtain a primary film material; S4: Perform tension heating pretreatment on the primary membrane material in both the transverse and longitudinal directions; S5: Simultaneous longitudinal and transverse stretching of the preheated membrane material to obtain a high-strength flame-retardant membrane with stable orientation structure. S6: The high-strength flame-retardant film is heat-set to stabilize its dimensions; S7: After heat setting, an electrically insulating coating is applied to the surface of the flame-retardant film, and the coating adhesion is enhanced by corona discharge treatment. S8: The flame-retardant film with completed surface treatment is subjected to static elimination and constant tension winding to obtain a high tensile strength PET flame-retardant film product for battery module insulation and fire protection.

[0024] The mass percentages of ethylene glycol phthalate chips, phosphorus-based reactive flame retardants, nanofillers, and chain extenders are as follows: 92% of the ethylene glycol phthalate slices were cut into pieces. Phosphorus-based reactive flame retardants: 5%; 2% nanofiller; Chain extender 1%; The nanofiller is selected from nano-alumina; the chain extender is selected from PBT glycol type chain extender.

[0025] S1 specifically includes: S11: Weigh out ethylene glycol phthalate chips, phosphorus-based reactive flame retardant, nanofiller and chain extender by mass percentage, and place them in a mixer at room temperature; S12: Set the mixer speed to 1000 rpm, turn on the stirring function, and continue mixing for 8 minutes, during which the material temperature is maintained at 45℃ to prevent the reactants from cross-linking prematurely; S13: Transfer the stirred material into a vacuum drying oven and dry it at 120℃ for 5 hours to remove adsorbed moisture and volatiles from the surface of the material and obtain a uniformly dried premixed modified material.

[0026] S2 specifically includes: S21: The premixed modified material is fed into a twin-screw reactive extruder, the temperature of each section of the extruder is set to 260℃, and a vacuum of -0.09MPa is applied to remove oligomers and volatiles; S22: Control the main screw speed of the extruder at 80 rpm to allow the material to melt and fully mix under the shearing of the screw, so that the phosphorus flame retardant and PET molecular chain can undergo a copolymerization reaction. S23: The material after the copolymerization reaction is completed is extruded from the die head, cooled and solidified by a cooling water bath at a temperature controlled at 20°C, and then modified PET copolymer particles with a particle size of 3mm are obtained by pelletizing.

[0027] S3 specifically includes: S31: Add the modified PET copolymer particles into a single-screw extruder, set the extrusion temperature to 260℃ and the screw speed to 60 rpm, so that they melt to form a uniform melt; S32: Molten material is extruded onto the casting roll through a wide T-shaped die. The die temperature is controlled at 270℃, and the surface temperature of the casting roll is controlled at 20℃. S33: Adjust the winding speed to 10 meters / minute, and wind the cooled and formed membrane material under constant tension to obtain a primary membrane material with a thickness of 20 micrometers.

[0028] S4 specifically includes: S41: The primary membrane material is passed sequentially through the longitudinal tension heating roller group. The roller surface temperature is set to 80℃, the membrane tension is controlled at 10N, and the membrane running speed is maintained at 15 meters / minute, so that it completes the tension heating treatment in the longitudinal direction. S42: The longitudinally processed membrane material is introduced into the transverse preheating box, the box temperature is controlled at 85℃, the transmission path is set to 4 meters, and the transverse tension is controlled at 8N by a tension traction device to complete the transverse tension heating treatment and obtain the pre-stretched membrane material with bidirectional prestress.

[0029] S5 specifically includes: S51: Before stretching, the membrane material is introduced into the synchronous biaxial stretching device, and the temperature of the membrane material is first raised to 100°C in the preheating zone to improve the mobility of molecular chains. S52: Apply longitudinal and transverse tensile forces to the membrane material simultaneously in the stretching zone. The longitudinal stretching ratio is set to 3.2 times, the transverse stretching ratio is set to 3.1 times, and the stretching rate is controlled at 70 meters per minute. S53: The stretched membrane material is introduced into the cooling zone through a fixed-width guide rail to rapidly reduce the membrane temperature to 50°C, thereby stabilizing the stretched structure and preventing dimensional shrinkage, resulting in a high-strength flame-retardant membrane with a thickness of 12 micrometers.

[0030] S6 specifically includes: S61: Introduce the high-strength flame-retardant film into the heat setting device, use an infrared heater to heat the film material in a non-contact manner, and set the setting temperature to 200℃. S62: Set a constant tension of 8N in the shaping zone and control the membrane material conveying speed to 15 meters / minute to keep the membrane surface taut and limit heat shrinkage deformation. S63: The continuous heating treatment time is controlled at 4 seconds. After the membrane material is output from the shaping area, it is introduced into the slow cooling section. The slow cooling temperature is set to 70℃ to complete the dimensional stabilization treatment of the high-strength flame-retardant membrane.

[0031] S7 specifically includes: S71: The heat-set high-strength flame-retardant film is transported to the coating station, and an electrically insulating coating is uniformly applied to one side of the film material by roller coating. The dry film thickness after coating is 0.8 micrometers. S72: Introduce the coated film into a hot air drying oven, set the drying temperature to 100℃ and the drying time to 4 minutes to complete the coating curing; S73: After drying, the membrane material is subjected to corona discharge treatment. The treatment voltage is set to 10kV and the treatment speed is 15m / min, so that the corona energy density on the surface of the membrane material reaches 1.2W·min / m², thus completing the polarization treatment of the surface of the electrically insulating coating.

[0032] S8 specifically includes: S81: The flame-retardant film with completed surface treatment is introduced into the electrostatic elimination device. The surface of the film is treated with AC high-voltage ion bars. The working voltage is set to 8kV and the action distance is controlled at 10cm to neutralize the accumulated charge on the surface of the film. S82: The flame-retardant film after static elimination is introduced into the winding station. The winding tension is set to 8N by the constant tension control system, and the winding speed is set to 12 meters / minute to complete the winding and collection of the flame-retardant film.

[0033] Example 2 S1: Weigh out 88% ethylene glycol phthalate chips, 7% phosphorus-based reactive flame retardant, 3% nanofiller (nano montmorillonite), and 2% chain extender (adipic acid-based chain extender) by mass percentage; add them to a mixer at room temperature, set the speed to 800 rpm, the stirring time to 5 minutes, and control the mixing temperature to 40℃; after mixing, transfer the material to a vacuum drying oven and dry it at 115℃ for 4 hours to remove adsorbed water and volatiles, and obtain the premixed modified material; S2: The dried premixed modified material is fed into a twin-screw reactive extruder. The temperature of each section is set to 240℃, the vacuum degree is controlled at -0.08MPa, and the main screw speed is set to 60 rpm. During the extrusion process, the flame retardant and PET undergo a melt copolymerization reaction. After the reaction is completed, the material is extruded through the die, cured in a 15℃ cooling water bath, and pelletized to obtain modified PET copolymer particles with a particle size of 2mm. S3: The modified PET granules are fed into a single-screw extruder, the extrusion temperature is set to 250℃ and the screw speed is 40 rpm to make the material melt evenly; after being extruded through the T-die at 255℃, it is directly cast onto a cooling roller with a roller temperature of 15℃, and the winding speed is controlled to be 6 meters / minute, finally obtaining a primary film material with a thickness of 15 micrometers. S4: The primary membrane material is sequentially introduced into the longitudinal tension heating roller group, with the roller surface temperature set at 70℃, the longitudinal tension controlled at 5N, and the running speed at 10 meters / minute; then it is introduced into the transverse preheating box, with the box temperature set at 70℃, the transmission path length at 3 meters, and the tension at 4N, to complete the bidirectional tension heating treatment and obtain the pre-stretched membrane material with prestress. S5: The pretreated membrane material is introduced into the biaxial stretching device. It is first heated to 90°C in the preheating zone, and then tensile forces in the longitudinal and transverse directions are applied simultaneously in the stretching zone. The longitudinal stretching ratio is 3.0 times and the transverse stretching ratio is 3.0 times. The stretching rate is controlled at 50 meters / minute. After stretching, it is immediately introduced into the cooling zone. The membrane material temperature drops to 40°C to obtain a high-strength flame-retardant membrane with a thickness of 8 micrometers. S6: The high-strength flame-retardant film is fed into the heat setting device, which uses an infrared heater for non-contact heating. The setting temperature is set at 180℃, the film tension is 5N, the conveying speed is 10 meters / minute, and the heating duration is 3 seconds. After setting, the film is introduced into the slow cooling section, and the slow cooling temperature is set at 60℃ to complete the dimensional stabilization treatment. S7: The shaped film material is introduced into the coating station, and an electrically insulating coating is applied to one side using a roller coating method. The dry film thickness of the coating is 0.5 micrometers. The film material is then placed in a hot air drying oven, and the drying temperature is set to 80℃ for 3 minutes to complete the curing. After drying, the film material is subjected to corona discharge treatment at a voltage of 6kV and a processing speed of 10 meters / minute. The corona energy density is controlled at 0.8W·min / m² to improve the coating adhesion. S8: The processed flame-retardant film is introduced into an electrostatic elimination device, which uses an AC high-voltage ion bar with a working voltage of 6kV and an action distance of 5cm to neutralize the surface charge. Finally, it is introduced into the winding station, where the winding tension is set to 5N and the winding speed is 8m / min. The constant tension winding and collection of the flame-retardant film is completed, and a high tensile strength PET flame-retardant film for battery module insulation and fire protection is obtained.

[0034] Example 3 S1: Weigh out 95.5% ethylene glycol phthalate chips, 3% phosphorus-based reactive flame retardant, 1% nanofiller (nano alumina), and 0.5% chain extender (PBT glycol chain extender) by mass percentage; add them to a mixer at room temperature, set the speed to 1200 rpm, the stirring time to 10 minutes, and control the mixing temperature to 50℃; after mixing, transfer the material to a vacuum drying oven and dry it at 125℃ for 6 hours to remove adsorbed water and volatiles, and obtain the premixed modified material; S2: The dried premixed modified material is fed into a twin-screw reactive extruder. The temperature of each section is set to 280℃, the vacuum degree is controlled at -0.095MPa, and the main screw speed is set to 120 rpm. During the extrusion process, the flame retardant and PET undergo a melt copolymerization reaction. After the reaction is completed, the material is extruded through the die, solidified in a 30℃ cooling water bath, and pelletized to obtain modified PET copolymer particles with a particle size of 4mm. S3: The modified PET granules are fed into a single-screw extruder, the extrusion temperature is set to 270℃ and the screw speed is 80 rpm to make the material melt evenly; after being extruded through the T-die at 275℃, it is directly cast onto a cooling roller with a roller temperature of 25℃, and the winding speed is controlled to be 12 m / min, finally obtaining a primary film material with a thickness of 25 microns. S4: The primary membrane material is sequentially introduced into the longitudinal tension heating roller group, with the roller surface temperature set to 90℃, the longitudinal tension controlled at 15N, and the running speed at 20 meters / minute; then it is introduced into the transverse preheating box, with the box temperature set to 95℃, the transmission path length at 6 meters, and the tension at 10N, to complete the bidirectional tension heating treatment and obtain the pre-stretched membrane material with prestress. S5: The pretreated membrane material is introduced into the biaxial stretching device. It is first heated to 110°C in the preheating zone, and then tensile forces in the longitudinal and transverse directions are applied simultaneously in the stretching zone. The longitudinal stretching ratio is 3.5 times and the transverse stretching ratio is 3.3 times. The stretching rate is controlled at 80 meters / minute. After stretching, it is immediately introduced into the cooling zone. The membrane material temperature drops to 60°C to obtain a high-strength flame-retardant membrane with a thickness of 15 micrometers. S6: The high-strength flame-retardant film is introduced into the heat setting device, which uses an infrared heater for non-contact heating. The setting temperature is set at 210℃, the film tension is 12N, the conveying speed is 20 meters / minute, and the heating duration is 6 seconds. After the setting is completed, it is introduced into the slow cooling section, and the slow cooling temperature is set at 80℃ to complete the dimensional stabilization treatment. S7: The shaped film material is introduced into the coating station, and an electrically insulating coating is applied to one side using a roller coating method. The dry film thickness of the coating is 1.0 micrometer. The film material is then placed in a hot air drying oven, and the drying temperature is set to 120℃ for 6 minutes to complete the curing. After drying, the film material is subjected to corona discharge treatment at a voltage of 12kV and a processing speed of 20 meters / minute. The corona energy density is controlled at 1.5W·min / m² to improve the coating adhesion. S8: The processed flame-retardant film is introduced into an electrostatic elimination device, using an AC high-voltage ion bar with a working voltage of 10kV and an action distance of 15cm to neutralize the surface charge; finally, it is introduced into the winding station, with the winding tension set at 12N and the winding speed at 15m / min, to complete the constant tension winding and collection of the flame-retardant film, and obtain a high tensile strength PET flame-retardant film product for battery module insulation and fire protection.

[0035] Comparative Example 1 Step 1: Weigh out 95% ethylene glycol phthalate chips, 4% bromine-based flame retardant, and 1% slip agent by mass percentage, add them to a high-speed mixer at room temperature, set the mixing speed to 600 rpm, and mix for 5 minutes. Step 2: The dry-mixed material is directly fed into a single-screw extruder. The extrusion temperature is set to 250℃ and the screw speed is 50 rpm. After the material melts, it is extruded through a flat die to the surface of a cooling roller at 30℃ for casting. The winding speed is 8 meters / minute to obtain a primary flame-retardant film with a thickness of 25 micrometers. Step 3: The film material is processed online by a calendering roller at a temperature of 70℃ and a linear pressure of 20 N / cm to improve surface smoothness and gloss. Then, it is directly wound up in a conventional manner to obtain the finished product.

[0036] Table 1 Comparison of Finished Product Performance Parameters Comparison Projects Example 1 Example 2 Example 3 Comparative Example 1 Longitudinal tensile strength (MPa) 220 195 210 125 Transverse tensile strength (MPa) 215 190 205 120 Tear strength (N / mm) 12.5 10.3 11.7 6.4 Oxygen Index (LOI, %) 34.2 32.5 33.1 24.8 Dimensional heat shrinkage rate (150℃ / 30min, %) 0.8 1.3 1.1 3.6 Surface resistivity (Ω·cm) <![CDATA[1.0×10¹ 4 ]]> 8.0×10¹³ 9.0×10¹³ 2.0×10¹² Coating adhesion rating (0~5, 0 is optimal) 0 1 0 4 Puncture breakdown voltage (kV, film thickness 12μm) 9.6 8.5 9 5.2 As shown in Table 1 above, Example 1 exhibits the best performance in terms of tensile strength, thermal stability, flame retardancy, electrical insulation, and surface treatment effect. In contrast, Comparative Example 1, lacking copolymerization modification, biaxial stretching, heat setting, and an electrical insulating coating, suffers from severely insufficient mechanical properties and thermal stability, failing to meet the technical requirements of high-end battery modules for flame-retardant film materials. Therefore, Example 1 represents the optimal implementation of this invention, achieving synergistic performance enhancement not only in its formulation structure but also in its systematic high-performance film material preparation process.

[0037] Table 2 Comparison of other performance parameters Comparison Projects Example 1 Example 2 Example 3 Comparative Example 1 Film breakage rate (times / 100,000 meters) 0 1 0 8 Tensile retention rate after heat aging (150℃×72h, %) 91.2 85.7 88.9 63.4 Flame retardant char residue (800℃, %) 19.5 16.8 18.2 9.7 Flatness deviation of the winding end face (mm) ±0.3 ±0.8 ±0.5 ±2.1 Corona treatment persistence (energy retention rate after 24 hours, %) 92.5 80.3 89.4 51.2 Coating thickness uniformity (standard deviation, μm) 0.06 0.12 0.08 0.35 Defect density on membrane surface (particles / m²) 3 8 5 21 As can be seen from Table 2 above, Example 1 showed the most stable performance in terms of film breakage rate, winding accuracy, corona persistence, and film surface cleanliness, reflecting good process continuity and compatibility with subsequent processing. The high values ​​of heat aging retention rate and flame retardant char rate indicate that it can still maintain good structural integrity and flame retardant performance at high temperatures. The coating thickness uniformity and film surface defect density are the lowest, further verifying its consistency and reliability in electrical insulation surface treatment.

[0038] In summary, Example 1 not only has the best performance indicators, but also outperforms other examples and comparative examples in terms of overall preparation stability, quality consistency and application reliability, making it suitable for long-term use in large-scale battery module manufacturing.

[0039] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules, characterized in that, Includes the following steps: S1: Weigh out ethylene glycol phthalate chips, phosphorus-based reactive flame retardant, nanofiller and chain extender according to the preset ratio, and mix them evenly to form a premixed modified material; S2: The premixed modified material undergoes a melt copolymerization reaction to form a modified PET copolymer; S3: The modified PET copolymer is melted and then cast to obtain a primary film material; S4: Perform tension heating pretreatment on the primary membrane material in both the transverse and longitudinal directions; S5: Simultaneous longitudinal and transverse stretching of the preheated membrane material to obtain a high-strength flame-retardant membrane. S6: The high-strength flame-retardant film is heat-set to stabilize its dimensions; S7: After heat setting, an electrically insulating coating is applied to the surface of the flame-retardant film, and the coating adhesion is enhanced by corona discharge treatment. S8: The flame-retardant film with completed surface treatment is subjected to static elimination and constant tension winding to obtain a high tensile strength PET flame-retardant film product for battery module insulation and fire protection.

2. The method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, The ethylene glycol phthalate chips, phosphorus-based reactive flame retardant, nanofiller, and chain extender are, by mass percentage, respectively: 88-95.5% ethylene glycol phthalate slices; Phosphorus-based reactive flame retardants: 3-7%; Nanofiller 1-3%; Chain extender 0.5-2%; The nanofiller is selected from nano-alumina or nano-montmorillonite; the chain extender is selected from PBT glycol-type chain extender or adipic acid-based chain extender.

3. The method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, S1 specifically includes: S11: Weigh out ethylene glycol phthalate chips, phosphorus-based reactive flame retardant, nanofiller and chain extender by mass percentage, and place them in a mixer at room temperature; S12: Set the mixer speed to 800-1200 rpm, turn on the stirring function, and continue mixing for 5-10 minutes, during which the material temperature is maintained at 40-50℃; S13: Transfer the stirred material into a vacuum drying oven and dry it at 115-125℃ for 4-6 hours to remove adsorbed moisture and volatiles from the surface of the material and obtain a uniformly dried premixed modified material.

4. The method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, S2 specifically includes: S21: The premixed modified material is fed into a twin-screw reactive extruder, the temperature of each section of the extruder is set to 240℃~280℃, and a vacuum of -0.08~-0.095MPa is applied to remove oligomers and volatiles; S22: Control the main screw speed of the extruder at 60-120 rpm to allow the material to melt and fully mix under the shearing of the screw, so that the phosphorus flame retardant and PET molecular chain can undergo a copolymerization reaction. S23: The material after copolymerization reaction is completed is extruded from the die head, cooled and solidified by a cooling water bath at a temperature controlled between 15℃ and 30℃, and then obtained as modified PET copolymer particles with a particle size of 2 to 4 mm by a pelletizing mechanism.

5. The method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, S3 specifically includes: S31: Add the modified PET copolymer particles into a single-screw extruder, set the extrusion temperature to 250℃~270℃, and the screw speed to 40~80 rpm, so that they melt to form a uniform melt; S32: The molten material is extruded onto the casting roller through a wide T-shaped die, with the die temperature controlled at 255℃~275℃ and the surface temperature of the casting roller controlled at 15℃~25℃; S33: Adjust the winding speed to 6-12 meters / minute, and wind the cooled and formed membrane material under constant tension to obtain a primary membrane material with a thickness of 15-25 micrometers.

6. The method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, S4 specifically includes: S41: Pass the primary membrane material through the longitudinal tension heating roller group in sequence. Set the roller surface temperature to 70℃~90℃, control the membrane tension to 5~15N, and maintain the membrane material running speed to 10~20 meters / minute, so that it can complete the tension heating treatment in the longitudinal direction. S42: The longitudinally processed membrane material is introduced into the transverse preheating box. The temperature of the box is controlled at 70℃~95℃, the transmission path is set to 3~6 meters, and the transverse tension is controlled at 4~10N by a tension traction device to complete the transverse tension heating treatment and obtain the pre-stretched membrane material with bidirectional prestress.

7. The method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 6, characterized in that, S5 specifically includes: S51: Before stretching, the membrane material is introduced into the synchronous biaxial stretching device, and the temperature of the membrane material is first raised to 90℃~110℃ in the preheating zone. S52: Apply longitudinal and transverse tensile forces to the membrane material simultaneously in the stretching zone. The longitudinal stretching ratio is set to 3.0 to 3.5 times, the transverse stretching ratio is set to 3.0 to 3.3 times, and the stretching rate is controlled to be 50 to 80 meters per minute. S53: The stretched membrane material is introduced into the cooling zone through a fixed-width guide rail, and the temperature of the membrane material is rapidly reduced to 40℃~60℃ to obtain a high-strength flame-retardant membrane with a thickness of 8~15 micrometers.

8. The method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, S6 specifically includes: S61: Introduce the high-strength flame-retardant film into the heat setting device, use an infrared heater to heat the film material in a non-contact manner, and set the setting temperature to 180℃~210℃. S62: Set a constant tension of 5-12N in the shaping zone and control the membrane material conveying speed to 10-20 meters / minute; S63: The continuous heating treatment time is controlled at 3 to 6 seconds. After the membrane material is output from the shaping area, it is introduced into the slow cooling section. The slow cooling temperature is set to 60℃ to 80℃ to complete the dimensional stabilization treatment of the high-strength flame-retardant membrane.

9. A method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, Specifically, S7 includes: S71: The heat-set high-strength flame-retardant film is conveyed to the coating station, and an electrically insulating coating is uniformly applied to one side of the film material by roller coating. The dry film thickness after coating is 0.5 to 1.0 micrometers. S72: Introduce the coated film into a hot air drying oven, set the drying temperature to 80℃~120℃, and the drying time to 3~6 minutes to complete the coating curing; S73: Perform corona discharge treatment on the dried membrane material. The treatment voltage is set to 6-12kV and the treatment speed is 10-20 m / min, so that the corona energy density on the membrane surface reaches 0.8-1.5W·min / m².

10. A method for preparing a high tensile strength PET flame-retardant film for insulation and fireproofing of battery modules according to claim 1, characterized in that, S8 specifically includes: S81: The flame-retardant film with completed surface treatment is introduced into the electrostatic elimination device. The surface of the film is treated with AC high-voltage ion bars. The working voltage is set to 6-10kV and the action distance is controlled at 5-15cm to neutralize the accumulated charge on the surface of the film. S82: The flame-retardant film after static elimination is introduced into the winding station. The winding tension is set to 5-12N by the constant tension control system, and the winding speed is set to 8-15 meters / minute to complete the winding and collection of the flame-retardant film.

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