Battery pack heat preservation foam with low compression strength

Abstract

The invention provides battery pack heat preservation foam with low compression strength. The problems that existing polyethylene foam is high in compression strength, insufficient in flame retardant property and the like in heat insulation, buffering and protection application of a new energy automobile battery pack are solved. The foam comprises the following components in parts by mass: 50-80 parts of low-density polyethylene, 10-20 parts of linear low-density polyethylene and 20-30 parts of ethylene-vinyl acetate copolymer as a resin matrix, 8-12 parts of azodicarbonamide, 1-3 parts of sodium carbonate and 1-3 parts of 4, 4 '-oxybisbenzenesulfonyl hydrazide are used as foaming agents; and 5-10 parts of a bromine-antimony flame retardant, 1-2 parts of a metallic soap lubricant and 1-3 parts of an antioxidant. The flame retardant grade of the foam reaches UL94HF-1, the compression strength is lower than 10kPa under 30% strain, and the aperture ratio of the foam is greater than or equal to 85%. The preparation method comprises the steps of internal mixing granulation, extrusion into sheets, irradiation crosslinking, heating foaming, physical rolling hole breaking and the like, and low compression strength, high aperture ratio and excellent flame retardance are realized by optimizing a resin blending system, a multi-stage foaming process and a physical rolling technology.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a battery pack thermal insulation foam with low compressive strength and a preparation method thereof, which is particularly suitable for heat insulation, buffering and protection of power batteries of new energy vehicles. Background Art

[0002] With the rapid development of new energy vehicles, the safety and performance stability of power batteries have become key concerns in the industry. During the charging and discharging process of power batteries, heat is generated, and different performances are exhibited at different ambient temperatures. High temperature may lead to thermal runaway of the battery, while low temperature will reduce the battery's cruising range and service life. Therefore, the thermal management of the battery pack is one of the core issues to ensure the safe operation of new energy vehicles.

[0003] Existing battery pack thermal insulation materials mostly use polyethylene foam. Although they have certain heat insulation and insulation properties, they have problems such as high compressive strength, poor resilience, and insufficient flame retardant performance, which easily lead to swelling, friction and damage of the battery soft pack, and pose a risk of thermal runaway. These materials cannot provide sufficient buffering when the battery expands, and are prone to becoming brittle in low-temperature environments, unable to effectively protect the battery. Traditional cross-linked polyethylene foam mostly uses a single resin matrix and a general foaming process, with a high closed-cell rate of the cell structure, making it difficult to meet the requirements of the battery pack for low compressive strength, high open-cell rate and flame retardant performance. In addition, the flame retardant performance of existing foam materials is generally low, unable to meet the strict requirements of new energy vehicles for battery safety. Summary of the Invention

[0004] The purpose of the present invention is to provide a battery pack thermal insulation foam with low compressive strength. By optimizing the resin blend system, multi-stage foaming process and physical rolling technology, the low compressive strength, high open-cell rate and excellent flame retardancy of the foam are achieved, significantly improving the thermal management safety and service life of the battery pack.

[0005] The formula of the present invention realizes low compressive strength, high open-cell rate, excellent flame retardant performance and good heat insulation and buffering performance through the optimization of the resin matrix, the combination of blowing agents and the synergistic effect of additives. This foam material can effectively solve the key problems of heat insulation, buffering and protection of new energy vehicle battery packs, and significantly improve the safety and service life of the battery pack.

[0006] The present invention provides a battery pack thermal insulation foam with low compressive strength, comprising the following components in parts by mass: 50 - 80 parts of low - density polyethylene, 10 - 20 parts of linear low - density polyethylene, and 20 - 30 parts of ethylene - vinyl acetate copolymer as the resin matrix; 8 - 12 parts of azodicarbonamide, 1 - 3 parts of sodium carbonate, and 1 - 3 parts of 4,4'-oxybis(benzenesulfonylhydrazide) as blowing agents; and 5 - 10 parts of bromine - antimony flame retardant, 0.5 - 2 parts of metal soap lubricant, and 1 - 3 parts of antioxidant as additives; wherein, the flame retardant grade of the foam reaches UL94 HF - 1, the compression strength is lower than 10 kPa at 30% strain, and the open - cell rate of the foam is greater than or equal to 85%.

[0007] The formulation of the battery - pack thermal - insulation foam with low compression strength of the present invention achieves low compression strength, high open - cell rate, excellent flame retardancy, and good heat - insulation and buffering properties through a carefully designed combination of components. First, low - density polyethylene has good flexibility and processing properties. It is the main matrix material of the foam, providing basic mechanical properties and forming ability. Its relatively low crystallinity makes it easy to form a cell structure during the foaming process, while providing a certain degree of elasticity and buffering properties. Linear low - density polyethylene has high strength and puncture resistance, while maintaining a certain degree of flexibility. After blending with low - density polyethylene, it can improve the comprehensive mechanical properties of the foam, enhance the tear resistance and durability of the foam, and optimize the uniformity of the cell structure. Ethylene - vinyl acetate copolymer has good flexibility, low - temperature resistance, and thermal stability, and also has a certain degree of adhesiveness and processing properties. In the foam, it can improve the flexibility and resilience of the foam, improve the performance of the foam in low - temperature environments, and promote the uniform formation of cells. Through the blending of low - density polyethylene, linear low - density polyethylene, and ethylene - vinyl acetate copolymer, a resin matrix with excellent flexibility, strength, and cell - forming ability is formed. This composite system can provide stable cell - wall support during the foaming process, and at the same time form an open - cell structure when the cells rupture, achieving the characteristics of low compression strength and high open - cell rate.

[0008] Second, azodicarbonamide is a commonly used chemical foaming agent with a relatively high decomposition temperature (about 200 - 220 °C). It releases nitrogen during decomposition, pushing the cell pores to expand; it provides the main gas source during the high-temperature stage (the second-stage foaming), enabling the cell pores to fully expand and form a stable cell structure. Sodium carbonate decomposes at a lower temperature (about 160 - 180 °C), releasing carbon dioxide gas; it provides the initial gas during the low-temperature stage (the first-stage foaming), forming initial cell nuclei and providing a basis for the subsequent foaming process. 4,4'-oxybis(benzenesulfonylhydrazide) is a foaming agent with a low decomposition temperature (about 190 - 200 °C), which releases gas during decomposition; it plays a role during the transition stage (the gradient temperature control stage), inhibiting the excessive expansion of cell pores, and at the same time causing partial rupture of the cell walls to form micro-channels, promoting the formation of an open-cell structure. Through the combination of the three foaming agents, a stepped foaming process is achieved. Sodium carbonate provides the initial cell nuclei during the low-temperature stage, 4,4'-oxybis(benzenesulfonylhydrazide) controls the rupture of the cell walls during the transition stage to form micro-channels, and azodicarbonamide pushes the cell pores to expand during the high-temperature stage, ultimately forming a foam structure with a high open-cell rate and low compressive strength.

[0009] Third, bromine-antimony flame retardants (such as the complex of antimony trioxide and decabromodiphenylethane) provide excellent flame retardant properties, enabling the flame retardant rating of the foam to reach UL94 HF-1; in the event of a fire, bromine-antimony flame retardants can effectively inhibit the spread of flames, reduce the fire risk, and ensure the safety of the battery pack. Metal soap lubricants (such as zinc oxide and zinc stearate) improve the processing performance, reduce the friction of the material during processing, and improve production efficiency; they reduce equipment wear during processing such as internal mixing and extrusion, and at the same time avoid local overheating caused by friction, ensuring the stability of the foaming agent. Antioxidants prevent the oxidative degradation of the resin during processing and use, extend the service life of the foam; improve the aging resistance of the foam, ensuring its stability and reliability during long-term use.

[0010] Through the optimization of the resin blending system and the physical rolling pore-breaking technology in the present invention, the foam can effectively absorb stress when compressed, reducing the friction risk during battery expansion; the open-cell structure helps to improve the heat insulation performance of the foam, reduce the thermal conductivity, while reducing the weight and enhancing the sound absorption effect; it meets the strict requirements of new energy vehicles for battery safety, reducing the fire risk.

[0011] In the low-compression-strength battery pack thermal insulation foam formulation of the present invention, the bromine-antimony flame retardant provides efficient flame retardancy through the synergistic effect of antimony trioxide and decabromodiphenylethane, enabling the flame retardancy rating of the foam to reach UL94 HF-1 while ensuring stability during processing and use. The metal soap lubricant provides good lubricity and thermal stability through the synergistic effect of zinc oxide and zinc stearate, improving the processing performance while ensuring the uniformity and stability of the material properties. The addition of these two additives not only enhances the flame retardancy and processing performance of the foam but also avoids negative impacts on the mechanical properties and foaming performance of the foam, making them an essential and important part of the formulation of the present invention.

[0012] In the raw material formulation of the low-compression-strength battery pack thermal insulation foam of the present invention, the bromine-antimony flame retardant is a composite of antimony trioxide and decabromodiphenylethane, with a mass ratio of 1:3-5; the metal soap lubricant includes 0.5-1 part of zinc oxide and 0.5-1 part of zinc stearate.

[0013] The bromine-antimony flame retardant is a composite composed of decabromodiphenylethane and antimony trioxide, with a mass ratio of 1:3-5. This composite flame retardant not only improves the flame retardancy rating of the foam (UL94 HF-1) but also ensures the stability of the material during processing and use, avoiding a decline in the foam properties caused by the addition of the flame retardant. By adjusting the ratio of antimony trioxide to decabromodiphenylethane, the flame retardant effect and processing performance can be optimized. Antimony trioxide, as a synergist, can improve the flame retardant efficiency of decabromodiphenylethane while reducing the amount of flame retardant used, avoiding negative impacts on the mechanical properties and processing performance of the material.

[0014] Antimony trioxide is a commonly used flame retardant synergist with good thermal stability and synergistic flame retardant effects; during combustion, antimony trioxide reacts with halogen compounds (such as bromides) to form antimony tribromide or halides of antimony trioxide. These compounds can capture free radicals in the gas phase, inhibit the propagation of the flame, thereby playing a flame retardant role and significantly improving the flame retardancy of the material, enabling the flame retardancy rating of the foam to reach UL94 HF-1.

[0015] Decabromodiphenylethane is an efficient brominated flame retardant with a high bromine content, capable of effectively inhibiting the spread of the flame; during combustion, decabromodiphenylethane decomposes to produce hydrogen bromide, which can capture free radicals in the combustion, thereby interrupting the combustion reaction chain. At the same time, the decomposition products of decabromodiphenylethane can also form a protective layer on the surface of the material, isolating oxygen and further inhibiting combustion. Decabromodiphenylethane provides the main flame retardant effect and, in synergistic action with antimony trioxide, makes the flame retardant effect more significant.

[0016] The metal soap lubricants include zinc oxide and zinc stearate, with a mass ratio of 0.5 - 1 part. By adjusting the ratio of zinc oxide and zinc stearate, the lubrication effect and processing performance can be optimized. Zinc oxide provides thermal stability and a synergistic flame retardant effect, while zinc stearate mainly provides lubrication and dispersion effects. The addition of metal soap lubricants not only improves the processing performance of the foam but also ensures the stability of the material during high-temperature processing, while avoiding a decrease in the properties of the foam due to the addition of lubricants. Zinc oxide is a multifunctional additive with lubricating, stabilizing, and synergistic flame retardant effects. During the processing, zinc oxide can reduce the friction between materials, improve the fluidity of the materials, reduce equipment wear, and at the same time has a certain thermal stability, which can prevent the degradation of the resin during high-temperature processing. It can also act synergistically with bromine-antimony flame retardants to further improve the flame retardant effect.

[0017] Zinc stearate is a common metal soap lubricant with good lubricity and dispersibility. During the processing, zinc stearate can reduce the friction between materials and equipment, improve the processing efficiency, and at the same time reduce energy consumption. Zinc stearate can improve the dispersibility of other additives (such as flame retardants, foaming agents, etc.) in the resin, ensuring the uniformity of the material properties. At the same time, zinc stearate has a certain thermal stability at high temperatures, which can prevent the material from decomposing due to local overheating during processing.

[0018] The preparation method of the low-compression-strength battery pack thermal insulation foam of the present invention prepares a battery pack thermal insulation foam with low compression strength, high open-cell rate, and excellent flame retardant performance by optimizing the resin blending system, multi-stage foaming process, and physical rolling technology. This kind of foam can effectively absorb the expansion stress during the charging and discharging process of the battery, reduce the friction risk between the batteries, and at the same time provide good heat insulation and buffering performance, ensuring the safety and service life of the new energy vehicle battery pack.

[0019] The preparation method of the low-compression-strength battery pack thermal insulation foam of the present invention specifically includes the following steps: S1 Internal mixer granulation: Mix the resin matrix with the foaming agent and additives, and carry out internal mixing at 120 - 150 °C for 20 - 30 minutes to prepare a blended granule with good dispersibility and processing performance, ensuring that all components (resin, foaming agent, flame retardant, etc.) are fully mixed during the internal mixing process to avoid uneven local components. Through internal mixing and granulation, the mixture is made into granules for subsequent processing; during the internal mixing process, the resin matrix begins to form a preliminary cross-linked structure, laying the foundation for subsequent foaming and cross-linking processes; the internal mixing temperature of 120 - 150 °C and the mixing time of 20 - 30 minutes ensure that the foaming agent and additives are evenly dispersed in the resin matrix, while avoiding premature decomposition of the foaming agent.

[0020] S2 extrusion into sheets: melt and extrude the blended particles through a single screw extruder, control the barrel temperature at 120-200°C, and the thickness of the extruded sheet is 2-5mm; melt the granular blend at high temperature to form a uniform melt; extrude into sheets through a T-die, control the sheet thickness to 2-5mm, and provide a suitable substrate for subsequent radiation cross-linking and foaming; the barrel temperature is 120-200°C to ensure good resin melting and avoid premature activation of the foaming agent; the sheet thickness is 2-5mm, which is convenient for subsequent process operations and ensures the final performance of the foam.

[0021] S3 irradiation cross-linking: The sheet is irradiated with an electron accelerator at a dose of 5-15kGy to form a cross-linking network and improve the mechanical properties and thermal stability of the material. Electron beam irradiation forms chemical bonds between the resin molecular chains, enhancing the strength and heat resistance of the material; the cross-linking network can support the pore structure and prevent the pores from breaking or deforming during the foaming process; the irradiation dose of 5-15kGy ensures a moderate degree of cross-linking to avoid excessive cross-linking that causes the material to become brittle.

[0022] S4 heating and foaming: The irradiated sheet is heated in two stages, using a stepped foaming method. The first stage is kept at 160-180°C for 3-5 minutes, and the second stage is kept at 200-220°C for 2-4 minutes to form an open-cell foam structure. In the first stage (160-180℃, 3-5 minutes), sodium carbonate decomposes at low temperature, releasing carbon dioxide to form initial cell nuclei; the formation of cell nuclei provides a basis for the subsequent foaming process, and the cell diameter is about 50-100μm; in the transition stage (190-200℃, 5-8 minutes), 4,4'-oxybisbenzenesulfonylhydrazine decomposes and releases gas, causing the cell wall to partially rupture to form microchannels; the rupture of the cell wall promotes the formation of an open-cell structure, laying the foundation for the final high open-cell rate; in the second stage (200-220℃, 2-4 minutes), azodicarbonamide decomposes, releasing a large amount of nitrogen, promoting the expansion of the cells, and finally forming cells with a diameter of 150-200μm; through the release of gas and the expansion of the cells, the final open-cell rate reaches more than 85%; stage-by-stage temperature control ensures that the foaming agent decomposes in sequence, achieving uniform formation of cells and optimization of the open-cell structure.

[0023] S5 physical rolling and puncturing: Use a double-roller rolling device to roll the foam to further destroy the closed-cell structure, increase the open-cell rate, reduce the compressive strength, and obtain a battery pack insulation foam with low compressive strength. In the multi-stage rolling, the pre-rolling initially destroys the closed-cell wall and reduces the initial compressive strength of the foam; the main rolling destroys the pore wall over a large area to further increase the open-cell rate; the final rolling eliminates the local unpunctured area to ensure the final performance of the foam. Through physical rolling, the compression strength of the foam at 30% strain is less than 10kPa, which meets the buffering and insulation requirements of the battery pack. By optimizing parameters such as roller diameter, speed ratio, and gap, the rolling effect and the final performance of the foam are ensured.

[0024] Through the synergistic effect of each step, the preparation method of the present invention has successfully realized a battery pack thermal insulation foam with low compression strength, high open-cell rate, excellent flame retardancy and heat insulation performance, meeting the safety and performance requirements of new energy vehicle battery packs. Among them, internal mixer granulation ensures the uniform mixing and preliminary cross-linking of each component, providing a good foundation for subsequent processes; extrusion into sheets forms sheets suitable for subsequent processing, controlling the thickness and uniformity; irradiation cross-linking enhances the mechanical properties and thermal stability of the material, providing stable cell support for the foaming process; heating and foaming realizes the uniform formation of cells and the optimization of the open-cell structure through a stepped foaming process; physical rolling and pore breaking further improves the open-cell rate, reduces the compression strength, and endows the foam with the final low compression strength and high heat insulation performance.

[0025] In the internal mixer granulation step of the low compression strength battery pack thermal insulation foam of the present invention, through carefully designed segmented operations, the uniform mixing, preliminary cross-linking and granulation of each component are ensured, providing high-quality blend granules for subsequent process steps. The main purpose of the internal mixer granulation step is to fully mix the resin matrix, blowing agent and additives to form a uniform blend, and through preliminary cross-linking and granulation, prepare granular materials suitable for subsequent processing. This process not only ensures the uniform dispersion of each component, but also optimizes the processing performance and final performance of the material by controlling the temperature and mixing time.

[0026] In the preparation method of the low compression strength battery pack thermal insulation foam of the present invention, the internal mixer granulation step specifically includes the following operations: S11 Raw material pretreatment: Crush the resin matrix including 50 - 80 parts of low-density polyethylene, 10 - 20 parts of linear low-density polyethylene, and 20 - 30 parts of ethylene-vinyl acetate copolymer to a particle size not exceeding 3 mm; the smaller particle size of the crushed resin matrix can better mix with the blowing agent and additives, avoiding uneven dispersion caused by too large particles; the smaller particle size helps to improve the fluidity and mixing efficiency of the materials during internal mixing, reducing problems such as local overheating or insufficient mixing; uniform resin matrix particles contribute to the formation of a uniform cell structure during subsequent foaming.

[0027] S12 Segmented feeding: The first stage: Put the pretreated resin matrix into an internal mixer for preliminary mixing, with an internal mixing temperature of 120 - 130 °C, a rotation speed of 20 - 30 rpm, and mix for 5 - 10 minutes; the lower temperature avoids premature decomposition of the blowing agent and ensures that the resin matrix can be fully melted; the lower rotation speed helps the uniform mixing of the resin matrix and avoids degradation caused by excessive shearing; mixing for 5 - 10 minutes ensures that the resin matrix is fully melted and forms a preliminary mixture, preparing for the subsequent addition of the blowing agent and additives.

[0028] Second stage: Add stepwise blowing agents including 8 - 12 parts of azodicarbonamide, 1 - 3 parts of sodium carbonate, 1 - 3 parts of 4,4'-oxybis(benzenesulfonylhydrazide) and additives including 5 - 10 parts of brominated antimony flame retardant, 0.5 - 1 part of zinc oxide, 0.5 - 1 part of zinc stearate, 1 - 3 parts of antioxidant. Heat up to 140 - 150 °C, increase the rotation speed to 40 - 50 rpm, and further knead for 15 - 20 minutes to form a uniform blend; the higher temperature helps the dispersion of blowing agents and additives in the resin matrix and promotes the preliminary cross-linking reaction; the higher rotation speed helps the uniform dispersion of blowing agents and additives and avoids uneven decomposition caused by excessive local concentration; kneading for 15 - 20 minutes ensures the full dispersion of blowing agents and additives to form a uniform blend and avoids premature decomposition of the blowing agent.

[0029] S13 Dynamic cross-linking: Keep the temperature at 150 °C ± 2 °C at the end of the internal mixer kneading and knead for 2 - 5 minutes for dynamic cross-linking; by controlling the temperature and kneading time, a preliminary cross-linked structure is formed in the resin matrix to enhance the mechanical properties and thermal stability of the material; the cross-linked structure can support the cell holes formed during the subsequent foaming process and prevent the cell holes from rupturing or deforming at high temperatures; the resin matrix after preliminary cross-linking has better stability during the subsequent processing and avoids degradation or deformation caused by high temperatures.

[0030] S14 Pelletizing and cooling: Extrude and pelletize the kneaded rubber compound through a twin-screw extruder, with the die head temperature at 160 - 170 °C and the pellet size at 2 - 4 mm to form granular materials. After water cooling to room temperature, dry them for standby; making the mixture into granular form facilitates the subsequent extrusion and sheet-forming process and improves the fluidity and processing efficiency of the material; controlling the die head temperature ensures good fluidity of the rubber compound during extrusion and avoids premature decomposition of the blowing agent; appropriate pellet size helps the uniformity of subsequent processing and avoids problems caused by over-sized or under-sized pellets; rapid cooling of the pellets by water cooling prevents pellet adhesion and removes surface moisture to ensure the dryness and stability of the pellets.

[0031] In the internal mixer kneading and pelletizing steps of the low compression strength battery pack thermal insulation foam of the present invention, through the synergistic effect of each step, not only the uniform mixing and preliminary cross-linking of each component are achieved, but also high-quality blended pellets are provided for the subsequent extrusion and sheet-forming, radiation cross-linking and foaming processes, ensuring the low compression strength, high open-cell rate and excellent heat insulation performance of the final foam. Among them, raw material pretreatment ensures the uniformity and good processability of the resin matrix; staged feeding through two-stage kneading ensures the uniform dispersion of blowing agents and additives in the resin matrix and avoids premature decomposition; dynamic cross-linking is carried out at the end of the internal mixer kneading to form a preliminary cross-linked structure, enhancing the mechanical properties and thermal stability of the material and providing support for the subsequent foaming process; pelletizing and cooling make the mixture into granular form for subsequent processing and ensure the stability and uniformity of the pellets through water cooling and drying.

[0032] In the kneading and granulation step of the present invention, dicumyl peroxide is added as a crosslinking accelerator, which shortens the crosslinking time, improves production efficiency, enhances the mechanical properties and thermal stability of the material, and can also improve the cell stability and reduce the compression strength through the supporting effect of the crosslinking network. At the same time, it acts synergistically with the flame retardant to improve the flame retardant performance.

[0033] In the method for preparing the battery pack thermal insulation foam with low compression strength of the present invention, the kneading and granulation step further includes: adding 0.1-0.5 parts of dicumyl peroxide as a crosslinking accelerator for mixing during the dynamic crosslinking process.

[0034] In the kneading and granulation step of the battery pack thermal insulation foam with low compression strength of the present invention, 0.1-0.5 parts of dicumyl peroxide is added as a crosslinking accelerator. When the amount is too small, the crosslinking reaction is insufficient and the expected crosslinking degree cannot be achieved; when the amount is too large, over-crosslinking occurs, making the material brittle and affecting the flexibility and processing performance of the foam. By controlling the addition amount of dicumyl peroxide, the best balance can be found between the crosslinking degree and the material properties, ensuring that the foam has good mechanical properties, thermal stability and low compression strength.

[0035] Dicumyl peroxide is a commonly used organic peroxide crosslinking agent, and its main function is to accelerate and promote the crosslinking reaction of the resin matrix. Dicumyl peroxide decomposes at high temperature to generate free radicals, which can initiate the chemical bonding between resin molecular chains to form a crosslinking network. By adding dicumyl peroxide, the crosslinking reaction time can be significantly shortened and the production efficiency can be improved. During the dynamic crosslinking process, the addition of dicumyl peroxide makes the crosslinking reaction more rapid and uniform, ensuring that the preliminary crosslinking is completed within a short time (2-5 minutes). At the same time, the free radicals generated by the decomposition of dicumyl peroxide have high activity and can effectively promote the crosslinking reaction between resin molecular chains to form a denser crosslinking network. Increasing the crosslinking degree can enhance the mechanical properties and thermal stability of the material, enabling the foam to have better cell support ability and dimensional stability during subsequent foaming and use.

[0036] During the foaming process, the crosslinked network can effectively support the cell structure and prevent the cells from rupturing or deforming under high temperature and gas pressure. Crosslinking is promoted by dicumyl peroxide, resulting in a more uniform and stable cell structure, thereby improving the thermal insulation and cushioning properties of the foam. To a certain extent, the crosslinked network restricts the excessive expansion of the cells. Meanwhile, during the physical rolling and pore-breaking process, the crosslinked structure can better withstand external forces and avoid excessive rupture of the cell walls. By optimizing the degree of crosslinking, the compression strength of the foam at 30% strain can be controlled below 10 kPa, meeting the requirement of low compression strength. The crosslinked network can improve the thermal stability of the material and reduce material decomposition and combustion caused by high temperature. Acting synergistically with bromine-antimony flame retardants, it further improves the flame retardancy of the foam, enabling it to reach the UL94 HF-1 flame retardant rating.

[0037] In the sheet extrusion step of the low-compression-strength battery pack thermal insulation foam of the present invention, through carefully designed temperature zone control, screw parameter adjustment, and sheet forming and cooling, the uniform extrusion and shaping of the sheet are ensured, providing a high-quality substrate for subsequent irradiation crosslinking and foaming processes. The main purpose of the sheet extrusion step is to melt and extrude the blended particles through a single-screw extruder to form a sheet with a certain thickness and uniformity. This process not only ensures the uniformity of the sheet but also, by controlling the temperature and pressure, avoids the premature activation of the blowing agent, laying the foundation for subsequent irradiation crosslinking and foaming processes.

[0038] In the preparation method of the low-compression-strength battery pack thermal insulation foam of the present invention, the sheet extrusion step specifically includes the following operations: S21 Temperature zone control: The barrel of the single-screw extruder is divided into four temperature zones, including a feeding zone at 120 - 140 °C, a compression zone at 150 - 170 °C, a homogenization zone at 180 - 190 °C, and a die head zone at 190 - 200 °C, to avoid premature activation of the blowing agent. The relatively low temperature in the feeding zone ensures that the blended particles do not melt prematurely during feeding, avoiding the activation of the blowing agent caused by high temperature. The gradually increasing temperature in the compression zone causes the resin matrix to start melting while avoiding premature decomposition of the blowing agent. The relatively high temperature in the homogenization zone ensures complete melting of the resin matrix to form a uniform melt. The highest temperature in the die head zone ensures good fluidity of the melt during extrusion while avoiding the activation of the blowing agent due to excessive temperature.

[0039] S22 Screw Parameter Adjustment: Control the screw rotation speed at 30 - 50 rpm, the length - diameter ratio at 25:1 - 30:1, and the head pressure at 8 - 12 MPa. A moderate screw rotation speed ensures the uniform mixing and extrusion of the melt, avoiding shear overheating caused by too high a rotation speed or uneven mixing caused by too low a rotation speed. An appropriate length - diameter ratio ensures the sufficient mixing and compression of the melt in the screw, while avoiding shear overheating caused by too large a length - diameter ratio or uneven mixing caused by too small a length - diameter ratio. An appropriate head pressure ensures good fluidity of the melt during extrusion, while avoiding melt fracture caused by too high a pressure or uneven extrusion caused by too low a pressure.

[0040] S23 Sheet Forming and Cooling: The melt is extruded into a sheet through a T - die. The opening of the die lip is 3 - 6 mm. The sheet is calendered and shaped by a three - roll calender, and the roll speed ratio is 1:1.05 - 1.1. After cooling, the sheet thickness is 2 - 5 mm. An appropriate opening ensures the uniform extrusion of the sheet, while avoiding the sheet being too thick due to too large an opening or too thin due to too small an opening. The sheet is calendered and shaped by the calender to ensure the flat surface and uniform thickness of the sheet. An appropriate roll speed ratio ensures that the sheet will not be stretched or compressed during the calendering process, maintaining the uniformity of the sheet. The sheet is cooled by a cooling roll to ensure good stability of the sheet in the subsequent irradiation cross - linking and foaming processes.

[0041] Through the synergistic effect of each step in the extrusion and sheet - forming process of the present invention, not only the uniform extrusion and shaping of the sheet are achieved, but also by controlling the temperature and pressure, the premature activation of the blowing agent is avoided, laying a foundation for the subsequent irradiation cross - linking and foaming processes. Among them, the temperature zone control ensures the uniformity of the melt and the stability of the blowing agent, avoiding premature activation; the screw parameter adjustment ensures the uniform mixing and extrusion of the melt, avoiding shear overheating or uneven mixing; the sheet forming and cooling ensure the uniformity and stability of the sheet, providing a high - quality substrate for the subsequent irradiation cross - linking and foaming processes.

[0042] In the method for preparing the low - compression - strength battery - pack thermal insulation foam of the present invention, in the irradiation cross - linking step, by precisely controlling the parameters of the irradiation equipment, the irradiation dose, and the irradiation method, the uniform cross - linking of the sheet is ensured, while avoiding the premature activation of the blowing agent. The main purpose of irradiation cross - linking is to form a cross - linked network between resin molecular chains through electron beam irradiation, thereby significantly improving the mechanical properties, thermal stability, and dimensional stability of the material. This process provides a stable substrate for the subsequent foaming process, ensuring the uniformity and stability of the cell structure, while avoiding the premature activation of the blowing agent caused by local overheating or uneven cross - linking.

[0043] In the method for preparing the low - compression - strength battery - pack thermal insulation foam of the present invention, the irradiation cross - linking step specifically includes the following operations: S31 Irradiation Equipment Parameter Setting: An industrial electron accelerator is used. The electron beam energy is 1 - 3 MeV, and the beam current intensity is 10 - 30 mA. The electron beam energy (1 - 3 MeV) ensures that the electron beam has sufficient energy to penetrate the sheet material, forming crosslinks between resin molecular chains. Excessive energy causes material degradation, while insufficient energy fails to achieve effective crosslinking. The beam current intensity (10 - 30 mA) controls the intensity of the electron beam, ensuring the efficiency and uniformity of the irradiation process. Excessive beam current intensity leads to local overheating, while too low intensity reduces the crosslinking efficiency.

[0044] S32 Irradiation Dose Control: Adjust the irradiation dose according to the sheet thickness. For a thickness of 2 - 3 mm, it corresponds to 5 - 8 kGy; for a thickness of 3 - 5 mm, it corresponds to 8 - 15 kGy. The dose rate is controlled at 2 - 5 kGy / s to avoid pre - foaming of the foam caused by local overheating. Adjust the irradiation dose according to the sheet thickness to ensure an appropriate degree of crosslinking. For a sheet with a thickness of 2 - 3 mm, it corresponds to 5 - 8 kGy, and for a sheet with a thickness of 3 - 5 mm, it corresponds to 8 - 15 kGy. Too low a dose results in insufficient crosslinking, while too high a dose makes the material brittle. Control the dose rate to avoid local overheating. An excessive dose rate causes the local temperature of the material to rise, thereby triggering premature activation of the foaming agent.

[0045] S33 S - shaped Dynamic Irradiation: The sheet passes through the irradiation area at a constant rate of 0.5 - 2 m / min, and the path is in an S - shaped reciprocating motion to ensure double - sided irradiation crosslinking. The degree of irradiation crosslinking is controlled at 60 - 80%. After irradiation, the sheet is immediately cooled to room temperature to avoid premature activation of the foaming agent caused by residual heat. The S - shaped reciprocating motion means that the sheet moves in an S - shaped path in the irradiation area, ensuring that the electron beam can evenly irradiate both sides of the sheet, avoiding uneven local crosslinking and improving the uniformity of crosslinking. Control the rate at which the sheet passes through the irradiation area to ensure the uniformity and consistency of the irradiation process. By precisely controlling the irradiation conditions, ensure that the degree of crosslinking is between 60 - 80%. An appropriate degree of crosslinking can improve the mechanical properties and thermal stability of the material, while avoiding embrittlement of the material. Immediately cool the sheet to room temperature after irradiation to avoid premature activation of the foaming agent caused by residual heat.

[0046] Through the synergistic effect of each step in the irradiation crosslinking process of the present invention, not only is uniform crosslinking of the sheet achieved, improving the mechanical properties and thermal stability of the material, but also premature activation of the foaming agent caused by local overheating or uneven crosslinking is avoided, providing a high - quality substrate for the subsequent foaming process. Among them, in the irradiation equipment parameter setting, by precisely controlling the electron beam energy and beam current intensity, the efficiency and uniformity of the irradiation process are ensured; adjust the irradiation dose and dose rate according to the sheet thickness to avoid local overheating and ensure an appropriate degree of crosslinking; ensure uniform double - sided crosslinking of the sheet through the dynamic irradiation method, and at the same time, avoid premature activation of the foaming agent through cooling measures.

[0047] In the preparation method of the low-compression-strength battery pack thermal insulation foam of the present invention, in the heating and foaming step, by controlling the temperature in stages during foaming, the uniform formation of pores, the optimization of the open-cell structure, and the stability of the final foam properties are achieved. The main purpose of the heating and foaming step is to achieve the uniform formation and expansion of pores by precisely controlling the temperature and time, and finally form a foam with low compression strength, high open-cell rate (≥85%), and excellent heat insulation performance. This process not only ensures the uniformity of the pore structure but also realizes the optimization of the open-cell structure by controlling the decomposition sequence of the blowing agent, laying a foundation for the subsequent physical rolling and pore-breaking process.

[0048] In the preparation method of the low-compression-strength battery pack thermal insulation foam of the present invention, the heating and foaming step specifically includes the following operations: S41 Low-temperature foaming in the first stage, forming initial pore nuclei through low-temperature foaming. The irradiated cross-linked sheet is vertically suspended in the foaming furnace, and nitrogen is introduced for protection to prevent the material from oxidizing at high temperatures and to avoid the interference of external air on the foaming process. The temperature is raised at a rate of 5-10 °C / min to 160-180 °C, causing sodium carbonate to decompose and release carbon dioxide to form initial pore nuclei, and maintaining the temperature for 3-5 minutes to ensure the full decomposition of sodium carbonate and the formation of uniform initial pore nuclei with a pore diameter of 50-100 μm.

[0049] S42 Gradient temperature control in the transition stage: The furnace temperature is evenly raised to 190-200 °C within 5-8 minutes to inhibit the concentrated decomposition of 4,4'-oxybis(benzenesulfonylhydrazide), and partial rupture of the pore walls forms micro-channels; in the temperature range of 190-200 °C, 4,4'-oxybis(benzenesulfonylhydrazide) begins to decompose, but its concentrated decomposition is inhibited by gradient heating to avoid excessive expansion or rupture of the pores; the time control of 5-8 minutes ensures that partial rupture of the pore walls forms micro-channels, providing gas channels for subsequent high-temperature foaming and promoting the formation of an open-cell structure.

[0050] S43 High-temperature foaming in the second stage, expanding the pores through high-temperature foaming to finally form an open-cell structure. The temperature is raised to 200-220 °C and maintained for 2-4 minutes to promote the complete thermal decomposition of azodicarbonamide to generate nitrogen, which drives the expansion of the pores. The release of nitrogen drives the pores to expand to a diameter of 150-200 μm, and the open-cell rate is increased to not less than 85%, and the final foam density is controlled to be 28-35 kg / m 3 ; Azodicarbonamide completely decomposes in the temperature range of 200-220 °C to generate nitrogen; the holding time of 2-4 minutes ensures the full decomposition of azodicarbonamide, the pore diameter expands to 150-200 μm, and the open-cell rate is increased to not less than 85%; at the same time, by controlling the foaming time and temperature, the density of the final foam is ensured to be within the target range, optimizing the heat insulation performance.

[0051] S44 Quenching and setting, locking the cell structure by spraying liquid nitrogen for cooling. After foaming, spray liquid nitrogen for cooling, and cool the foam to below 80°C at a rate of 15 - 20°C / s to lock the cell structure, with the compression strength not exceeding 10 kPa. Rapid cooling can effectively lock the cell structure and prevent the cells from shrinking or deforming during cooling. The cooling temperature is below 80°C to ensure the stability of the cell structure after cooling. The final compression strength of the foam does not exceed 10 kPa, meeting the requirement of low compression strength.

[0052] Through the synergistic effect of each step in the heating and foaming process of the present invention, not only the uniform formation and expansion of cells are achieved, but also the open-cell structure is optimized by controlling the decomposition sequence and temperature of the blowing agent. Finally, a battery pack thermal insulation foam with low compression strength, high open-cell rate and excellent thermal insulation performance is prepared. Among them, the low-temperature foaming in the first stage forms initial cell nuclei through the decomposition of sodium carbonate, providing a basis for the subsequent foaming process; the gradient temperature control in the transition stage inhibits the concentrated decomposition of 4,4'-oxybis(benzenesulfonylhydrazide), causing partial rupture of the cell walls to form micro-channels, creating conditions for the formation of the open-cell structure; the high-temperature foaming in the second stage generates nitrogen through the decomposition of azodicarbonamide, promoting the expansion of cells, and finally forming a cell structure with a high open-cell rate (≥85%); quenching and setting locks the cell structure through rapid cooling, ensuring the low compression strength and high thermal insulation performance of the foam.

[0053] In the method for preparing a battery pack thermal insulation foam with low compression strength of the present invention, the physical rolling and pore-breaking step further destroys the cell walls by mechanical rolling, increases the open-cell rate of the foam, reduces the compression strength, and thus endows the foam with excellent thermal insulation performance and buffering performance.

[0054] The main purpose of the physical rolling and pore-breaking step is to transform the foam with a closed-cell structure into an open-cell structure through multi-stage rolling, while controlling the compression strength and cell diameter of the foam. This process not only increases the open-cell rate of the foam (≥85%), but also ensures the low compression strength of the foam (not exceeding 10 kPa), enabling it to effectively absorb the expansion stress in the new energy vehicle battery pack, reducing the risk of friction between batteries, and providing good thermal insulation performance at the same time.

[0055] In the method for preparing a battery pack thermal insulation foam with low compression strength of the present invention, the physical rolling and pore-breaking step specifically includes the following operations: Set the parameters of the S51 rolling equipment to ensure that the equipment can meet the requirements of foam rolling. Adopt a double-roller rolling device with a roller diameter of 200 - 300 mm. The larger roller diameter can provide stable rolling pressure to ensure uniform stress on the foam during rolling. The surface hardness is HRC55 - 60. The high-hardness roller surface can effectively transfer pressure to ensure the bursting effect of the cell walls. The thickness of the hard chromium plating layer on the roller surface is 0.1 - 0.3 mm. The hard chromium layer can improve the wear resistance and corrosion resistance of the roller and extend the service life of the equipment. The adjustment range of the roller gap is 0.1 - 1 mm. The adjustable gap range can adapt to foams of different thicknesses to ensure the rolling effect. The roller speed ratio is 1:1.2 - 1.5. The appropriate speed ratio can ensure that the foam does not slip or accumulate during rolling. The linear speed matches the foam conveying rate at 0.5 - 2 m / min. The linear speed matching the foam conveying speed can ensure the continuity and stability of the rolling process.

[0056] S52 Multi-stage rolling control. Gradually break the cell walls through multi-stage rolling to increase the open-cell rate and avoid a decrease in foam performance caused by over-rolling. Pre-rolling: Set the roller gap to 80 - 90% of the foam thickness to initially break the closed-cell walls and prepare for the subsequent main rolling; the pressure is 0.5 - 1 MPa. The lower pressure avoids excessive damage to the cell structure. Main rolling: Adjust the gap to 50 - 70% of the foam thickness to further narrow the gap and promote large-area bursting of the cell walls; the pressure is increased to 1.5 - 2.5 MPa. The higher pressure ensures the bursting of the cell walls and the open-cell rate is increased to not less than 85%. Final rolling: Further narrow the gap to 30 - 50% of the foam thickness to eliminate local unbroken cell areas and ensure a uniform open-cell rate; the pressure is 2.5 - 3 MPa. The highest pressure ensures the complete bursting of the cell walls and avoids a decrease in foam performance caused by over-rolling.

[0057] S53 Post-treatment and slitting. Ensure the dimensional stability and final performance of the foam through cooling and shaping and slitting. After rolling, the foam is shaped by a cooling roller with a water temperature of 10 - 15 °C. The residual stress in the foam is eliminated through the cooling roller to ensure the dimensional stability and performance consistency of the foam. Slit into the target size with a compressive strength not exceeding 10 kPa to ensure the low compressive strength of the foam so that it can effectively absorb the expansion stress in the battery pack; the cell diameter is 150 - 200 μm. Through rolling and cooling and shaping, ensure that the cell diameter is within the target range to optimize the heat insulation performance.

[0058] Through the synergistic effect of each step, the physical rolling and pore-forming process of the present invention not only achieves a high open-cell rate (≥85%) and low compression strength (not exceeding 10 kPa) of the foam, but also ensures the heat insulation performance and buffering performance of the foam, enabling it to effectively absorb expansion stress in the new energy vehicle battery pack, reducing the risk of friction between batteries, and ensuring the safety and service life of the battery pack. Among them, the equipment parameters are set by precisely setting the roller diameter, hardness, coating thickness, gap adjustment range and speed ratio to ensure that the equipment can meet the requirements of multi-stage rolling; the multi-stage rolling control gradually destroys the cell walls and improves the open-cell rate through the step-by-step control of pre-rolling, main rolling and final rolling, while avoiding the decline of foam performance caused by excessive rolling; the post-treatment and slitting ensure the dimensional stability and final performance of the foam through cooling and shaping and slitting, so as to meet the application requirements of the new energy vehicle battery pack.

[0059] In the preparation method of the low-compression-strength battery pack thermal insulation foam of the present invention, the double-roller rolling device is the key equipment for realizing physical rolling and pore-forming. It transforms the foam with a closed-cell structure into a foam with a high open-cell rate by precisely controlling the rolling parameters, while ensuring the low compression strength and uniform cell structure of the foam. The main function of the double-roller rolling device is to destroy the closed-cell structure of the foam through mechanical pressure to form a foam network with a high open-cell rate, thereby reducing the compression strength of the foam and improving its heat insulation performance and buffering performance. This device is the key equipment for realizing the low compression strength and high open-cell rate of the foam.

[0060] In the method for preparing the battery pack thermal insulation foam with low compression strength of the present invention, the diameter range of the rollers of the double-roller rolling device used is 200 - 300 mm. A larger roller diameter can provide a larger contact area and a more stable rolling pressure, ensuring uniform stress on the foam during rolling and avoiding excessive local pressure resulting in excessive rupture of the foam pores. The surface hardness of the rollers is HRC55 - 60. The high-hardness roller surface can effectively transmit pressure, ensuring the rupture effect of the foam pore walls. At the same time, the high-hardness material can improve the wear resistance and service life of the rollers, reducing the equipment maintenance cost. The thickness of the hard chromium plating layer on the roller surface is 0.1 - 0.3 mm. The hard chromium layer has high hardness and good corrosion resistance, which can further improve the wear resistance and service life of the rollers, and at the same time reduce the adhesion between the foam and the roller surface during rolling. The adjustment range of the roller gap is 0.1 - 1 mm. The adjustable gap range can adapt to foams of different thicknesses, ensuring precise control of pressure and gap during the rolling process at different stages (pre-rolling, main rolling, final rolling), and achieving the effect of gradually breaking the pores. The roller speed ratio is 1:1.2 - 1.5. An appropriate speed ratio can ensure that the foam does not slip or accumulate during rolling, while ensuring the continuity and uniformity of the foam. The design of the speed ratio can effectively control the conveying speed and rolling effect of the foam. The wire speed matching range is 0.5 - 2 m / min. The wire speed matching the foam conveying speed can ensure the continuity and stability of the rolling process, avoiding foam deformation or accumulation caused by speed mismatch.

[0061] The double-roller rolling device gradually destroys the foam pore walls through multi-stage rolling. The roller gap for pre-rolling is 80 - 90% of the foam thickness, and the pressure is 0.5 - 1 MPa, initially destroying the closed pore walls to prepare for the subsequent main rolling, while avoiding excessive destruction of the foam pore structure. The roller gap for main rolling is 50 - 70% of the foam thickness, and the pressure is 1.5 - 2.5 MPa, further narrowing the gap to cause large-area rupture of the foam pore walls, and increasing the open pore rate to not less than 85%. The roller gap for final rolling is 30 - 50% of the foam thickness, and the pressure is 2.5 - 3 MPa, eliminating local unbroken pore areas to ensure uniform open pore rate, while avoiding performance degradation of the foam caused by excessive rolling.

[0062] Post-treatment and slitting eliminate the residual stress in the foam through a cooling roller, ensuring the dimensional stability and performance consistency of the foam, ensuring the low compression strength of the foam, enabling it to effectively absorb the expansion stress in the battery pack, and ensuring that the foam pore diameter is within the target range through rolling and cooling shaping, optimizing the heat insulation performance.

[0063] The precise control of the parameters of the double-roller rolling device of the present invention ensures a high open-cell rate (≥85%) and a low compression strength (not exceeding 10 kPa) of the foam. Through multi-stage rolling and post-treatment processes, the heat insulation performance and buffering performance of the foam are significantly improved, enabling it to effectively absorb the expansion stress of the battery, reduce the risk of friction between batteries, and ensure the safety and service life of the new energy vehicle battery pack.

[0064] In summary, the present invention has the following beneficial effects: 1. The present invention adopts a resin blend system of low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymer, which is different from the single low-density polyethylene matrix in traditional foams. This composite formulation optimizes the melt strength and flexibility of the foam through the synergistic effect of different resins, achieving the characteristics of low compression strength and high open-cell rate, and at the same time improving the comprehensive performance of the foam; the present invention uses a multi-foaming agent combination of azodicarbonamide, sodium carbonate, and 4,4'-oxybisbenzenesulfonyl hydrazide, which is different from the use of a single foaming agent in traditional foams. By utilizing the decomposition temperature and kinetic characteristics of different foaming agents, a stepped foaming process is realized, effectively controlling the formation and rupture of cells, and finally forming a foam structure with a high open-cell rate and low compression strength; the present invention adopts a composite flame retardant of antimony trioxide and decabromodiphenylethane, combined with metal soap lubricants (zinc oxide, zinc stearate), which is different from the use of a single flame retardant and lubricant in traditional foams, avoiding the negative impact on the resilience of the foam while improving the flame retardant performance. 2. Different from traditional foams, the present invention realizes a low compression strength of less than 10 kPa under 30% strain of the foam by optimizing the resin ratio, foaming agent combination, and additive system, which can effectively absorb the expansion stress during the charging and discharging process of the battery and reduce the risk of cell friction; through the synergistic effect of multiple foaming agents and the physical rolling and pore-breaking process, the open-cell rate of the foam of the present invention is ≥85%. Combined with the liquid nitrogen quenching and setting process, the cell structure is locked, significantly improving the heat insulation performance and stabilizing the internal temperature of the battery pack; at the same time, the flame retardant grade of the battery pack thermal insulation foam of the present invention reaches UL94 HF-1, with a wide temperature resistance range and strong chemical corrosion resistance, which can adapt to complex working conditions and ensure the long-term safe operation of the battery pack. 3. The present invention realizes breakthrough performances of a foam open-cell rate ≥85% and a compression strength ≤10 kPa through a stepped foaming process (temperature-controlled foaming in stages), S-shaped dynamic irradiation cross-linking (double-sided uniform irradiation), and double-roller multi-stage rolling and pore-breaking technology (step-by-step destruction of the closed-cell structure), combined with the liquid nitrogen quenching and setting process. At the same time, the production efficiency is optimized, ensuring the comprehensive improvement of the flame retardancy (UL94 HF-1) and temperature resistance of the material, reducing the production cost, and enhancing the market competitiveness of the product, providing a high-safety and high-stability heat insulation and buffering solution for the new energy vehicle battery pack. Description of the Drawings

[0065] Figure 1 It is a schematic diagram of the production process of a battery pack thermal insulation foam with low compression strength. Specific implementation mode

[0066] This specific embodiment is only an interpretation of the present invention, and it is not a limitation of the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

[0067] Example 1

[0068] Formulation composition: Resin matrix: 70 parts of low-density polyethylene, 15 parts of linear low-density polyethylene, 25 parts of ethylene-vinyl acetate copolymer Foaming agent: 10 parts of azodicarbonamide, 2 parts of sodium carbonate, 2 parts of 4,4'-oxybisbenzenesulfonyl hydrazide Flame retardant: 8 parts of a complex of antimony trioxide and decabromodiphenylethane (mass ratio 1:4) Auxiliary agent: 0.8 part of zinc oxide, 0.7 part of zinc stearate, 2 parts of antioxidant (1010) Preparation method: S1 Kneading and pelletizing: Feed in two stages, knead at 140 °C for 25 minutes, and add 0.3 part of dicumyl peroxide to promote crosslinking; S2 Extruding into sheets: The four-zone temperature of the single-screw extruder is (130 °C / 160 °C / 185 °C / 195 °C), the screw speed is 40 rpm, and the sheet thickness is 3 mm; S3 Irradiation crosslinking: The electron beam energy is 2 MeV, the dose is 10 kGy, and S-shaped dynamic irradiation is carried out, with a crosslinking degree of 70%; S4 Heating and foaming: The first stage: Keep warm at 170 °C for 4 minutes, and carbon dioxide forms initial pores with a diameter of 80 μm; The second stage: Keep warm at 210 °C for 3 minutes, and nitrogen pushes the pores to expand to 180 μm, with an open cell rate of 87%; S5 Physical rolling and pore breaking: Use a double-roll rolling device to roll the foam until the pore diameter reaches 170 μm, and obtain a battery pack thermal insulation foam with low compression strength.

[0069] Example 2

[0070] Formulation composition: Resin matrix: 60 parts of low-density polyethylene, 20 parts of linear low-density polyethylene, 20 parts of ethylene-vinyl acetate copolymer Foaming agent: 9 parts of azodicarbonamide, 1.5 parts of sodium carbonate, 2.5 parts of 4,4'-oxybisbenzenesulfonyl hydrazide Flame retardant: 10 parts of a complex of antimony trioxide and decabromodiphenylethane (mass ratio 1:3) Auxiliaries: 1 part of zinc oxide, 0.5 part of zinc stearate, 1.5 parts of antioxidant (1010) Preparation method: S1 Kneading and pelletizing: Kneading at 150 °C for 22 minutes, 0.2 part of crosslinking accelerator; S2 Extruding into sheets: Four-zone temperature of single-screw extruder (130 °C / 160 °C / 180 °C / 190 °C), screw speed 35 rpm; S3 Irradiation crosslinking: Dose 8 kGy, crosslinking degree 65%; S4 Heating and foaming: The first stage is to keep warm at 165 °C for 5 minutes, and the second stage is to keep warm at 205 °C for 2 minutes; S5 Physical rolling and pore formation: Using a double-roll rolling device to roll the foam until the pore diameter reaches 180 μm; Other operations are the same as in Example 1 to obtain a battery pack thermal insulation foam with low compressive strength.

[0071] Example 3

[0072] Formulation composition: Resin matrix: 80 parts of low-density polyethylene, 10 parts of linear low-density polyethylene, 30 parts of ethylene-vinyl acetate copolymer Foaming agent: 12 parts of azodicarbonamide, 3 parts of sodium carbonate, 1 part of 4,4'-oxybisbenzenesulfonyl hydrazide Flame retardant: 6 parts of a complex of antimony trioxide and decabromodiphenylethane (mass ratio 1:5) Auxiliaries: 0.5 part of zinc oxide, 1 part of zinc stearate, 3 parts of antioxidant (1010) Preparation method: S1 Kneading and pelletizing: Kneading at 130 °C for 30 minutes, 0.5 part of crosslinking accelerator; S2 Extruding into sheets: Four-zone temperature of single-screw extruder (130 °C / 160 °C / 190 °C / 200 °C), screw speed 45 rpm; S3 Irradiation crosslinking: Dose 15 kGy, crosslinking degree 75%; S4 Heating and foaming: The first stage is to keep warm at 180 °C for 3 minutes, and the second stage is to keep warm at 220 °C for 4 minutes; S5 Physical rolling and pore formation: Using a double-roll rolling device to roll the foam until the pore diameter reaches 175 μm; Other operations are the same as in Example 1 to obtain a battery pack thermal insulation foam with low compressive strength.

[0073] Example 4

[0074] Formulation composition: Resin matrix: 80 parts of low-density polyethylene, 20 parts of linear low-density polyethylene, 30 parts of ethylene-vinyl acetate copolymer Foaming agent: 12 parts of azodicarbonamide, 3 parts of sodium carbonate, 3 parts of 4,4'-oxybis(benzenesulfonylhydrazide) Flame retardant: 10 parts of a complex of antimony trioxide and decabromodiphenylethane (mass ratio 1:3) Auxiliary agent: 1 part of zinc oxide, 1 part of zinc stearate, 3 parts of antioxidant (1010) Preparation method: S1 Kneading and granulating: Feeding in two stages, kneading at 150 °C for 30 minutes, adding 0.5 part of dicumyl peroxide to promote crosslinking; S2 Extruding into sheets: Four-zone temperature of single-screw extruder (140 °C / 170 °C / 190 °C / 200 °C), screw speed 50 rpm; S3 Irradiation crosslinking: Electron beam energy 5 MeV, dose 15 kGy, S-shaped dynamic irradiation, crosslinking degree 80%; S4 Heating and foaming: First stage: Keep warm at 180 °C for 5 minutes, carbon dioxide forms initial pores with a diameter of 100 μm; Second stage: Keep warm at 220 °C for 4 minutes, nitrogen pushes the pores to expand to 200 μm, and the open-cell rate is 90%; S5 Physical rolling and pore breaking: Use a double-roll rolling device to roll the foam until the pore diameter reaches 200 μm; Other operations are the same as in Example 1 to obtain a battery pack thermal insulation foam with low compressive strength.

[0075] Example 5

[0076] Formulation composition: Resin matrix: 50 parts of low-density polyethylene, 10 parts of linear low-density polyethylene, 20 parts of ethylene-vinyl acetate copolymer Foaming agent: 8 parts of azodicarbonamide, 1 part of sodium carbonate, 1 part of 4,4'-oxybis(benzenesulfonylhydrazide) Flame retardant: 5 parts of a complex of antimony trioxide and decabromodiphenylethane (mass ratio 1:5) Auxiliary agent: 0.5 part of zinc oxide, 0.5 part of zinc stearate, 1 part of antioxidant (1010) Preparation method: S1 Kneading and granulating: Feeding in two stages, kneading at 120 °C for 20 minutes, adding 0.1 part of dicumyl peroxide to promote crosslinking; S2 Extruding into sheets: Four-zone temperature of single-screw extruder (120 °C / 150 °C / 180 °C / 190 °C), screw speed 30 rpm; S3 Irradiation crosslinking: Electron beam energy 1 MeV, dose 5 kGy, S-shaped dynamic irradiation, crosslinking degree 60%; S4 Heating and foaming: First stage: Keep warm at 130 °C for 3 minutes, carbon dioxide forms initial pores with a diameter of 50 μm; The second stage: Keep the temperature at 200 °C for 2 minutes, and use nitrogen to expand the cell pores to 150 μm with an open cell rate of 85%; S5 Physical rolling to break pores: Use a double-roller rolling device to roll the foam until the cell pore diameter reaches 150 μm; Other operations are the same as in Example 1 to obtain a battery pack thermal insulation foam with low compressive strength.

[0077] Comparative Example 1 Formulation composition: Resin matrix: 100 parts of pure low-density polyethylene Blowing agent: 15 parts of azodicarbonamide Flame retardant: Not added Auxiliaries: 0.5 part of zinc oxide and 0.5 part of zinc stearate Preparation method: After mixing and granulating, directly extrude into sheets without irradiation cross-linking; Single-stage foaming, keep the temperature at 200 °C for 5 minutes; Without physical rolling step; Other operations are the same as in Example 1 to obtain a battery pack thermal insulation foam.

[0078] Comparative Example 2 Formulation composition: Resin matrix: 70 parts of low-density polyethylene, 15 parts of linear low-density polyethylene, and 25 parts of ethylene-vinyl acetate copolymer Blowing agent: 10 parts of azodicarbonamide Flame retardant: 8 parts of a complex of antimony trioxide and decabromodiphenylethane (1:4) Auxiliaries: The same as in Example 1 Preparation method: Without staged foaming, directly keep the temperature at 200 °C for 7 minutes; Without liquid nitrogen quenching, natural cooling; Other operations are the same as in Example 1 to obtain a battery pack thermal insulation foam.

[0079] Comparative Example 3 Formulation composition Same as the formulation in Example 1.

[0080] Preparation method: Directly cool after foaming without double-roller rolling; Other operations are the same as in Example 1 to obtain a battery pack thermal insulation foam.

[0081] 1. Performance testing Perform performance testing on the battery pack thermal insulation foams with low compressive strength prepared in Examples 1-5 and the battery pack thermal insulation foams prepared in Comparative Examples 1-3, including the compressive strength, open cell rate, flame retardancy, and heat insulation performance of the foam.

[0082] The following are the detection methods for the compressive strength, open cell rate, flame retardancy, and heat insulation performance of the foam, and each detection method is described in one paragraph: 1.1 Compressive strength Testing method: The compression strength test is used to evaluate the mechanical properties of the foam under compression to determine its buffering capacity. The foam sample is cut into standard sizes and placed between the upper and lower pressing plates of a universal material testing machine. Pressure is applied to the sample at a constant compression rate, and the compression stress value at 30% strain is recorded. The lower this value, the smaller the compression strength of the foam and the better its buffering performance.

[0083] 1.2 Open-cell rate Testing method: The open-cell rate test is used to evaluate the cell structure characteristics of the foam and is observed through an optical microscope or a scanning electron microscope (SEM). First, cross-sectional samples are taken from multiple different positions of the foam sample and prepared into thin slices suitable for microscopic observation. The cell structure is observed under magnification in the microscope, and the number of open cells and closed cells is counted. The open-cell rate is calculated by the ratio of the number of open cells to the total number of cells, and the result is expressed as a percentage. A high open-cell rate usually means better heat insulation and buffering performance.

[0084] 1.3 Flame retardancy Testing method: The flame retardancy test is used to evaluate the fire prevention ability of the foam through the horizontal burning test of the UL94 standard. The foam sample is cut into standard sizes and horizontally fixed in the combustion test device. One end of the sample is ignited, and the flame propagation speed, burning time, and self-extinguishing ability of the sample are observed. The flame retardancy grade is evaluated based on the burning speed and self-extinguishing time. The foam that reaches the UL94 HF-1 grade indicates that it can effectively inhibit flame propagation and reduce the fire risk in case of a fire.

[0085] 1.4 Heat insulation performance Testing method: The heat insulation performance test is used to evaluate the heat conduction ability of the foam and is carried out by the heat flow meter method. The foam sample is sandwiched between a hot plate and a cold plate. The hot plate maintains a constant temperature (50 °C), and the cold plate maintains a lower temperature (0 °C). The heat flux density passing through the foam is measured by a heat flow meter, and the thermal conductivity is calculated in combination with the thickness and area of the sample. The lower the thermal conductivity, the better the heat insulation performance of the foam, which can effectively reduce heat transfer and stabilize the internal temperature of the battery pack.

[0086] 1.5 Density detection The foam sample is cut into regular cubes or cuboids, its volume is accurately measured, and at the same time, the mass of the sample is weighed using an electronic balance to calculate the sample density. The test results are expressed in kg / m 3 It indicates that the lower the density, the higher the degree of lightweight of the foam.

[0087] 2. Test results Summary table of performance test results of each group of foam samples

[0088] Result analysis: In the performance test of compressive strength, the compressive strengths of Examples 1-5 were between 7.5-9.2 kPa, all lower than 10 kPa, meeting the requirement of low compressive strength, indicating that through the optimization of the formula and process (such as multi-foaming agent combination, physical rolling to break pores, etc.), the foam can effectively absorb stress and exhibit good buffering performance. The compressive strength of Comparative Example 1 was 12.0 kPa, significantly higher than that of the examples, indicating that the traditional polyethylene foam has poor buffering performance due to the lack of optimized formula and process. The compressive strength of Comparative Example 2 was 10.5 kPa, slightly higher than that of the examples. Due to the lack of foaming agents such as sodium carbonate and 4,4'-oxybis(benzenesulfonyl hydrazide), the cell structure was not uniform enough, resulting in a decline in buffering performance. The compressive strength of Comparative Example 3 was 9.8 kPa, close to but slightly higher than that of the examples. The lack of physical rolling led to insufficient optimization of the cell structure, affecting the buffering performance.

[0089] Therefore, it can be obtained that in the battery pack thermal insulation foam with low compressive strength of the present invention, the optimized formula and process (multi-foaming agent combination and physical rolling) significantly reduce the compressive strength of the foam and improve the buffering performance.

[0090] In the detection of the open cell ratio, the open cell ratios of Examples 1-5 were between 85%-90%, all higher than 85%, indicating that through the physical rolling to break pores process, a large number of open cell structures were formed in the foam, which is beneficial to reducing the compressive strength and improving the heat insulation performance. The open cell ratio of Comparative Example 1 was only 60%, indicating that the traditional polyethylene foam has a mainly closed cell structure due to the lack of optimized process, resulting in poor heat insulation and buffering performance. The open cell ratio of Comparative Example 2 was 75%, lower than that of the examples. Due to the lack of foaming agents such as sodium carbonate and 4,4'-oxybis(benzenesulfonyl hydrazide), the cell structure was not uniform enough, resulting in a decrease in the open cell ratio. The open cell ratio of Comparative Example 3 was 80%. Without physical rolling, the open cell ratio was lower than that of the examples, indicating that physical rolling is the key process to improve the open cell ratio.

[0091] Therefore, it can be obtained that in the preparation of the battery pack thermal insulation foam with low compressive strength of the present invention, the physical rolling to break pores process and the multi-foaming agent combination significantly increase the open cell ratio of the foam and optimize the heat insulation and buffering performance.

[0092] In the flame retardancy performance test, the flame retardancy ratings of Examples 1-5 are all UL94 HF-1, indicating that by adding bromine-antimony flame retardants (antimony trioxide and decabromodiphenylethane), the foam can effectively inhibit flame propagation and meet the flame retardancy requirements of new energy vehicle battery packs. In Comparative Example 1, no flame retardant was added, and the flame retardancy performance did not pass the UL94 test, indicating that traditional polyethylene foam poses a high risk in case of fire. The flame retardancy rating of Comparative Example 2 is UL94 V-2, slightly lower than that of the examples, because the lack of blowing agents such as sodium carbonate and 4,4'-oxybisbenzenesulfonyl hydrazide results in an uneven cell structure, affecting the dispersion and effectiveness of the flame retardant. The flame retardancy rating of Comparative Example 3 is UL94 HF-1, the same as that of the examples, indicating that even without physical rolling, the addition of the flame retardant can still ensure a certain flame retardancy performance.

[0093] Therefore, it can be concluded that in the formulation of the battery pack thermal insulation foam with low compression strength of the present invention, the addition of bromine-antimony flame retardants is the key to improving the flame retardancy performance of the foam, while the combined blowing agents and the physical rolling process have less influence on the flame retardancy performance, but there is still room for optimization.

[0094] In the heat insulation performance test, the thermal conductivity coefficients of Examples 1-5 are between 0.033 and 0.037 W / (m·K), all lower than 0.04 W / (m·K), showing good heat insulation performance, mainly due to the high open cell rate and the optimized cell structure, which reduce heat transfer. The thermal conductivity coefficient of Comparative Example 1 is 0.045 W / (m·K), significantly higher than that of the examples, indicating that traditional polyethylene foam has poor heat insulation performance due to its low open cell rate. The thermal conductivity coefficient of Comparative Example 2 is 0.040 W / (m·K), slightly higher than that of the examples, because the lack of blowing agents such as sodium carbonate and 4,4'-oxybisbenzenesulfonyl hydrazide results in an uneven cell structure and a decrease in heat insulation performance. The thermal conductivity coefficient of Comparative Example 3 is 0.038 W / (m·K), close to that of the examples but slightly higher. The lack of physical rolling leads to an unoptimized cell structure and slightly poor heat insulation performance.

[0095] Therefore, it can be concluded that in the battery pack thermal insulation foam with low compression strength of the present invention, the high open cell rate and the optimized cell structure significantly reduce the thermal conductivity coefficient of the foam and improve the heat insulation performance. The physical rolling and pore-forming process in the preparation method is the key factor.

[0096] In the density test, the density range of Examples 1-5 is 28-30 kg / m 3 , all lower than 35 kg / m 3, indicating that through the optimization of the formulation and process (such as the combination of multiple blowing agents, physical rolling to break holes, etc.), the foam achieved good lightweight effects while maintaining excellent heat insulation and cushioning properties. The low density indicates that the foam significantly reduced the weight while maintaining good mechanical properties, which helps to reduce the overall weight of the new energy vehicle battery pack, improve energy efficiency and cruising range. The combination of low density and high open-cell rate further optimized the heat insulation performance and reduced heat transfer. The density of Comparative Example 1 was 35 kg / m 3 , which was significantly higher than that of the examples, indicating that the traditional polyethylene foam lacked an optimized formulation. The density of Comparative Example 2 was 34 kg / m 3 , slightly higher than that of the examples, indicating that the lack of blowing agents such as sodium carbonate and 4,4'-oxybis(benzenesulfonyl hydrazide) led to an uneven cell structure, slightly higher density and a decline in heat insulation performance. The density of Comparative Example 3 was 33 kg / m 3 , close to that of the examples but slightly higher, because physical rolling was not carried out, resulting in an unoptimized cell structure, slightly higher density and slightly poorer heat insulation performance.

[0097] Generally speaking, the present invention provides a battery pack thermal insulation foam with low compressive strength. Through the combination of multiple blowing agents, the addition of bromine-antimony flame retardant and the physical rolling to break holes process in its formulation and preparation method, the compressive strength, open-cell rate, flame retardant performance and heat insulation performance of the foam have been significantly improved. The examples have excellent comprehensive performance through the optimization of the formulation and process, and can meet the strict requirements of new energy vehicle battery packs for heat insulation, cushioning and flame retardant performance. The traditional polyethylene foam performs poorly in terms of compressive strength, open-cell rate, flame retardant performance and heat insulation performance due to the lack of optimized formulation and process. The lack of the combination of multiple blowing agents in the comparative examples led to an uneven cell structure, a decline in compressive strength, open-cell rate and heat insulation performance, slightly poorer flame retardant performance, and the lack of physical rolling led to slightly poorer open-cell rate and heat insulation performance.

Claims

1. A battery pack insulation foam with low compression strength, characterized in that: The invention comprises the following components in parts by weight: 50-80 parts of low-density polyethylene, 10-20 parts of linear low-density polyethylene, and 20-30 parts of ethylene-vinyl acetate copolymer as a resin matrix; 8-12 parts of azodicarbonamide, 1-3 parts of sodium carbonate, 1-3 parts of 4,4'-oxybisbenzenesulfonyl hydrazide are used as foaming agents; and 5-10 parts of bromine antimony flame retardant, 1-2 parts of metal soap lubricant, 1-3 parts of antioxidant are used as auxiliary agents; wherein the flame retardant grade of the foam reaches UL94HF-1, the compressive strength is less than 10kPa under 30% strain, and the foam opening rate is greater than or equal to 85%.

2. The low compression strength battery pack insulation foam according to claim 1, characterized in that: The bromine antimony flame retardant is a complex of antimony trioxide and decabromodiphenylethane, with a mass ratio of 3:1-5:1; the metal soap lubricant includes zinc oxide and zinc stearate, with a mass ratio of 1:2-2:

1.

3. The low compression strength battery pack insulation foam according to claim 1, characterized in that: The preparation method specifically comprises the following steps: S1 mixing and granulation: mixing the resin matrix with the foaming agent and the additive, mixing at 120-150°C for 20-30 minutes to prepare the blended particles; S2 extrusion into sheets: the blended particles are melted and extruded through a single screw extruder, the barrel temperature is controlled at 120-200°C, and the thickness of the extruded sheet is 2-5mm; S3 irradiation cross-linking: The sheet is irradiated with an electron accelerator at a dose of 5-15 kGy to form a cross-linked network; S4 heating and foaming: the irradiated sheet is heated in two stages, using a stepped foaming method, with the first stage being 160-180°C for 3-5 minutes, and the second stage being 200-220°C for 2-4 minutes to form open-cell foam; S5 physical rolling and puncturing: Use a double roller rolling device to roll the foam to obtain a battery pack insulation foam with low compression strength.

4. The method for preparing the thermal insulation foam for battery pack with low compression strength according to claim 3, characterized in that: The mixing and granulation step specifically includes the following operations: S11 Raw material pretreatment: crush low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymer to a particle size not exceeding 3 mm; S12 staged feeding: First stage: put the pretreated resin matrix into internal mixing, with a rotation speed of 20-30rpm and mixing at 120-130℃ for 5-10 minutes; The second stage: add foaming agent and additives, raise the temperature to 140-150℃, increase the speed to 40-50rpm, and mix for 15-20 minutes; S13 dynamic crosslinking: maintain 150℃±2℃ at the end of mixing, and mix for 2-5 minutes; S14 granulation and cooling: the rubber compound after internal mixing is extruded into granules by a twin-screw extruder, the die temperature is 160-170℃, the pellet size is 2-4mm, and it is cooled to room temperature and then dried for use.

5. The method for preparing the thermal insulation foam for battery pack with low compression strength according to claim 4, characterized in that: The mixing and granulation step further comprises: adding 0.1-0.5 parts of dicumyl peroxide as a crosslinking accelerator for mixing during the dynamic crosslinking process.

6. The method for preparing the thermal insulation foam for battery pack with low compression strength according to claim 3, characterized in that: The extrusion into sheets step specifically comprises the following operations: S21 temperature zoning control: the barrel of the single screw extruder is divided into four temperature zones, including a feed zone at 120-140°C, a compression zone at 150-170°C, a homogenization zone at 180-190°C, and a die zone at 190-200°C, to avoid premature activation of the foaming agent; S22 screw parameter adjustment: control the screw speed to 30-50rpm, the aspect ratio to 25:1-30:1, and the die pressure to 8-12MPa; S23 sheet forming and cooling: The melt is extruded into sheets through a T-die with a die lip opening of 3-6mm; the sheet is calendered and shaped by a three-roll calender with a roller speed ratio of 1:1.05-1.

1. The thickness of the sheet after cooling is 2-5mm.

7. The method for preparing the thermal insulation foam for battery pack with low compression strength according to claim 3, characterized in that: The radiation cross-linking step specifically includes the following operations: S31 irradiation equipment parameter setting: using industrial electron accelerator, electron beam energy is 1-3MeV, beam intensity is 10-30mA; S32 irradiation dose control: adjust the irradiation dose according to the thickness of the sheet, 2-3mm thickness corresponds to 5-8kGy, 3-5mm thickness corresponds to 8-15kGy, and the dose rate is controlled at 2-5kGy / s to avoid local overheating and foam pre-foaming; S33 S-shaped dynamic irradiation: The sheet passes through the irradiation area at a constant speed of 0.5-2m / min, and the path is S-shaped reciprocating motion to ensure double-sided irradiation cross-linking. The irradiation cross-linking degree is controlled at 60-80%. After irradiation, the sheet is immediately cooled to room temperature to avoid residual heat triggering the activation of the foaming agent.

8. The method for preparing the thermal insulation foam for battery pack with low compression strength according to claim 3, characterized in that: The heating and foaming step specifically includes the following operations: S41 first stage low temperature foaming: hang the radiation cross-linked sheet vertically in the foaming furnace, introduce nitrogen protection and heat to 160-180℃, keep warm for 3-5 minutes, so that the sodium carbonate decomposes to release carbon dioxide, forming initial cell nuclei with a cell diameter of 50-100μm; S42 transition stage gradient temperature control: the furnace temperature is evenly raised to 190-200°C within 5-8 minutes to inhibit the concentrated decomposition of 4,4'-oxybisbenzenesulfonylhydrazine, and the pore wall is partially broken to form microchannels; S43 second stage high temperature foaming: heating to 200-220℃, keeping warm for 2-4 minutes, to promote the complete thermal decomposition of azodicarbonamide to generate nitrogen. The release of nitrogen promotes the expansion of the pores to a diameter of 150-200μm, and the open porosity is increased to no less than 85%, controlling the final foam density to 28-35kg / m 3 ; S44 rapid cooling and shaping: After foaming is completed, liquid nitrogen spray cooling is used to cool the foam to below 80°C at a rate of 15-20°C / s to lock the pore structure, and the compression strength does not exceed 10kPa.

9. The method for preparing the thermal insulation foam for battery pack with low compression strength according to claim 3, characterized in that: The physical rolling and breaking step specifically includes the following operations: S51 rolling equipment parameter setting: double roller rolling device, roller diameter is 200-300mm, surface hardness is HRC55-60, roller surface hard chrome plating thickness is 0.1-0.3mm, roller gap adjustment range is 0.1-1mm, roller speed ratio is 1:1.2-1.5, line speed matching foam conveying rate is 0.5-2m / min; S52 multi-stage rolling control: Pre-rolling: roller gap is set to 80-90% of foam thickness, pressure is 0.5-1MPa, initially destroying the closed cell wall; Main rolling: gap is adjusted to 50-70% of foam thickness, pressure is increased to 1.5-2.5MPa, causing large-scale rupture of cell walls, and the open cell rate is increased to no less than 85%; Final rolling: gap is further reduced to 30-50% of foam thickness, pressure is 2.5-3MPa, eliminating local unbroken areas; S53 finishing and slitting: After rolling, the foam is shaped by cooling rollers at a water temperature of 10-15°C to eliminate residual stress; it is slit to the target size, with a compression strength not exceeding 10kPa and a cell diameter of 150-200μm.

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