A copolyamide hot melt adhesive film for power batteries and a preparation method thereof

Abstract

This invention discloses a copolyamide hot melt adhesive film for power batteries and its preparation method. The method includes melting a copolyamide base resin under an inert atmosphere at 90–120°C, homogenizing it in the molten state to form a base melt; heating the base melt to 120–130°C, adding an interface conditioning component, and stirring to obtain a premixed intermediate; heating the premixed intermediate to 130–140°C, adding a crystallization inducing component, dispersing for 15–35 minutes, and degassing to obtain a hot melt adhesive film intermediate; extruding the hot melt adhesive film intermediate at 120–170°C to form a continuous film preform, followed by heat treatment and reshaping, and cooling to obtain the copolyamide hot melt adhesive film for power batteries. This film maintains good dimensional stability and deformation recovery, which is beneficial for maintaining the interfacial support stability of the power battery adhesive layer or encapsulation layer during long-term use.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a copolyamide hot melt adhesive film for power batteries and its preparation method. Background Technology

[0002] With the continuous development of new energy vehicles and energy storage systems, the integration of power batteries in cells, modules, and battery packs is constantly increasing, placing higher demands on the comprehensive performance of adhesive and encapsulation materials. Hot melt adhesive films, due to their solvent-free nature, ease of die-cutting, suitability for continuous bonding processes, and ability to balance structural connections and partial encapsulation, have been gradually applied in power batteries for fixing insulating components, connecting buffer layers, edge encapsulation, and interface bonding between various dissimilar materials. In these applications, hot melt adhesive films not only need to meet the hot-pressing requirements during assembly but also need to withstand complex conditions such as continuous pressure, localized temperature rise, thermal cycling, and multi-material interface constraints during long-term battery use. Therefore, their structural retention capability and interface stability under service conditions become crucial factors affecting the overall reliability of power batteries.

[0003] Existing hot melt adhesive films for bonding or encapsulating power batteries typically meet bonding requirements by adjusting softening temperature, initial tack, melt flowability, or interlayer adhesion. In actual use of power batteries, hot melt adhesive films are often under constant pressure and repeatedly experience fluctuations in operating temperature and changes in local stress. The adhesive film is prone to slow deformation accumulation, which gradually reduces the local thickness and causes stress distribution to shift, thereby affecting the stability of the interface support.

[0004] Therefore, there is a need to provide a copolyamide hot melt adhesive film for power batteries and its preparation method to solve the problem that existing hot melt adhesive films for power batteries are prone to creep, which affects the stability of interface support. Summary of the Invention

[0005] The main objective of this invention is to provide a copolyamide hot melt adhesive film for power batteries and its preparation method, aiming to solve the technical problems mentioned in the background section.

[0006] The present invention adopts the following technical solution: A copolyamide hot melt adhesive film for power batteries and its preparation method, comprising: S1: Take the copolyamide base resin and heat it to 90-120°C under an inert atmosphere to melt it. In the molten state, homogenize it to form a base melt. The base melt has a two-stage response characteristic. S2: Heat the base melt to 120-130°C, add the interface conditioning component and stir to obtain a premixed intermediate; S3: Heat the premixed intermediate to 130-140°C, add the crystallization induction component, disperse for 15-35 minutes, keep warm for 5-15 minutes, and then degas to obtain the hot melt adhesive film intermediate; S4: The hot melt adhesive film intermediate is extruded at 120-170°C to form a continuous film preform, and then heat-treated and re-formed in sequence. After cooling, a copolyamide hot melt adhesive film for power batteries is obtained.

[0007] Further, step S1 includes: The copolyamide base resin is placed in a reaction vessel and heated to 90-110°C under a nitrogen atmosphere, and kept at the temperature for 20-30 minutes to obtain a molten copolyamide base resin. The copolyamide base resin is kept in a molten state at 90-120°C, and the stirring speed is adjusted to 150-300 rpm. The mixture is continuously stirred for 20-40 minutes to homogenize it, resulting in a base melt with a two-stage response characteristic. The two-stage response characteristic is that the base melt maintains flowable wetting ability during the heating stage and forms cohesive support ability during the cooling stage.

[0008] Further, in step S1, the copolyamide base resin includes at least two copolyamide resins with different crystallization tendencies and molecular weight distributions, including aliphatic copolyamide, semi-aromatic copolyamide, amino-terminated copolyamide, and carboxyl-terminated copolyamide.

[0009] Further, step S2 includes: Under an inert atmosphere, the base melt is kept at 100-120°C, the interface conditioning component is added, the stirring speed is adjusted to 200-400 rpm, and the mixture is stirred for 10-20 minutes to obtain the first mixture; Heat the first mixture to 120-130°C, add the flow conditioning component, and continue stirring for 5-15 minutes while maintaining the speed to obtain the second mixture; Adjust the stirring speed to 150 rpm, and degas the second mixture under a vacuum of -0.04 to -0.09 MPa for 5 to 15 minutes to obtain a premixed intermediate.

[0010] Further, in step S2, the interface conditioning component includes at least one of anhydride grafted polymer, polyimide modified resin and amide-containing block copolymer, and the flow conditioning component includes at least one of fatty acid amide, hydroxy fatty acid ester and long-chain fatty acid glyceride.

[0011] Further, step S3 includes: Under an inert atmosphere, the premixed intermediate was kept at 130–140°C for 5–10 minutes. The crystallization inducing component was added, and the stirring speed was adjusted to 300–800 rpm. The mixture was dispersed for 10–20 minutes to obtain the mixed intermediate. Add at least one of heat-resistant oligomers or surface-modified microparticles to the mixed intermediate, increase the stirring speed to 600-1000 rpm, and continue to disperse for 5-15 minutes to form a mixture; The mixture is kept at 130-140℃ for 5-15 minutes and then degassed for 5-10 minutes under a vacuum of -0.03 to -0.08 MPa to obtain a hot melt adhesive film intermediate.

[0012] Further, in step S3, the crystallization inducing component is an organic nucleating agent, which includes at least one of amide nucleating agents, aromatic carboxylate nucleating agents, and heterocyclic crystallization promoters; the heat-resistant oligomer includes at least one of polyimide oligomers, polyarylate oligomers, and aromatic polyamide oligomers; and the surface-modified inorganic particles include at least one of silica, talc, and alumina that have been surface-treated with silane coupling agents, titanate coupling agents, or aluminate coupling agents.

[0013] Further, step S4 includes: The hot melt adhesive film intermediate is fed into an extrusion film forming device and extruded and cast at 120-170°C to form a continuous film preform. The continuous film preform is subjected to a first heat treatment at 80-120℃ for 5-8 minutes, and then the temperature is raised to 120-140℃ for a second heat treatment of 5-10 minutes. The continuous film preform after the second heat treatment is subjected to low-tension re-conditioning, cooled to room temperature, and surface stabilization treatment to obtain a copolyamide hot melt adhesive film for power batteries.

[0014] A copolyamide hot melt adhesive film for power batteries is prepared by the preparation method of a copolyamide hot melt adhesive film for power batteries as described in any of the preceding claims.

[0015] Beneficial effects: In this invention, the copolyamide base resin is first melted and homogenized under an inert atmosphere to form a base melt with a two-stage response characteristic. An interface-modifying component is then added to coordinate the spreading behavior and interfacial contact state of the base melt, resulting in a more uniform contact layer in the premixed intermediate during film formation. This allows for the formation of a more continuous support region within the adhesive layer, better thickness retention under localized pressure, and more balanced interfacial stress. Furthermore, a crystallization-inducing component is introduced into the premixed intermediate at a higher temperature. After dispersion, heat treatment, and degassing, a hot melt adhesive film intermediate is formed. The film structure is then refined through extrusion, heat treatment, and refining processes, promoting a uniform microstructure within the film and reducing the impact of residual defects and localized stress concentrations during film formation on subsequent service conditions. This maintains good dimensional stability and deformation recovery capability, suppressing slow deformation accumulation, thus contributing to the interfacial support stability and structural consistency of the power battery adhesive layer or encapsulation layer during long-term use. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a method for preparing a copolyamide hot melt adhesive film for power batteries according to the present invention. The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0017] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. To make the objectives, technical solutions, and advantages of the invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0018] Reference Figure 1 This invention proposes a method for preparing a copolyamide hot melt adhesive film for power batteries, comprising: S1: Take the copolyamide base resin and heat it to 90-120°C under an inert atmosphere to melt it. In the molten state, homogenize it to form a base melt. The base melt has a two-stage response characteristic. In step S1, not only is the copolyamide base resin heated and melted, but a base resin system that can simultaneously consider film-forming processability and service stability is also established at the starting point of preparation. Here, "copolyamide base resin" refers to the copolyamide material existing as the main phase of the hot melt adhesive film. Its molecular chain contains different structural units, making it easier to adjust the softening range, melt flowability, and crystallization behavior compared to single polyamides. Specifically, two types of copolyamides with different chain segment regularity and different crystallization tendencies can be preferably blended. One type has higher molecular chain flexibility, making it easier to form a stable melt flow during the melting stage at 90–120°C, thus providing a better wetting and spreading foundation for the bonding process; the other type has a relatively higher crystallization driving force, enabling faster establishment of crystalline support structures during cooling. The inert atmosphere reduces the possibility of thermo-oxidative degradation, end-group side reactions, or molecular weight fluctuations of the copolyamide during the heating stage, thereby maintaining a more stable molecular chain state of the base resin during melting.

[0019] Upon reaching the molten state, homogenization enables the different copolyamide components to form a relatively uniform dispersion at the melt level. This ensures that the softening characteristics, melt viscosity, and crystallization potential of each component reach a level where they can work synergistically within the same system. The resulting "base melt" can be understood as a unified matrix upon which all components can be further introduced. It must possess the rheological basis suitable for adding interface-modifying components, while also retaining the material potential to form an ordered microstructure after the subsequent addition of crystallization-inducing components. The two-stage response characteristic refers to the base melt's ability to maintain suitable fluidity during the heated bonding stage to facilitate sufficient contact between the melt and the bonded interface, while gradually forming cohesive support as the temperature decreases, allowing the material to transition from a flowable state to a stable, shaped state.

[0020] S2: Heat the base melt to 120-130°C, add the interface conditioning component and stir to obtain a premixed intermediate; In step S2, assuming the base melt already possesses a stable melting range and a two-stage response, the melt undergoes interface adaptation treatment, transforming it from a "film-forming resin melt" into a "functionalized melt suitable for interface bonding in power batteries." Interface modifiers are additives or modifiers that regulate melt polarity distribution, interfacial wetting behavior, and local flow states. Their purpose is not simply to reduce viscosity, but to facilitate easier spread and formation of a continuous contact layer when the melt contacts metal parts, insulating sheets, or composite separators without significantly weakening the copolyamide's bulk support capacity. Further increasing the temperature to 120–130°C serves two purposes: firstly, to maintain a more fully flowing state in the base melt, facilitating uniform diffusion of the interface modifiers within the system; and secondly, to prevent insufficient local mixing due to excessively low temperatures, which could affect the consistency of the interfacial layer during film formation. During stirring and mixing, the interface modifiers preferentially distribute to the amorphous regions of the copolyamide melt and near the phase boundaries between different chain segments, allowing the entire melt to maintain its bulk skeleton potential while achieving more compliant and controllable interfacial contact characteristics. Because the interface modifiers are redistributed within the melt to meet the needs of contact layer formation and micro-gap filling, the melt can more fully penetrate the small uneven areas on the surfaces of common battery-bound materials during thermal bonding, thus reducing the problem of local contact discontinuities. Simultaneously, this interface modulation does not alter the two-stage response foundation established in the previous step; that is, the material still possesses appropriate flow and spreading capabilities during heating, and can still gradually establish cohesive support based on the host resin after cooling. The resulting premixed intermediate retains the material basis required for the subsequent formation of a stable support layer and provides a uniform carrier for the introduction of crystallization-inducing components in the next step. This allows microstructure control to be established on a more stable contact layer and a more consistent melt state, thereby enabling the entire preparation process to gradually transition from interface adaptation to internal structure refinement.

[0021] S3: Heat the premixed intermediate to 130-140°C, add the crystallization induction component, disperse for 15-35 minutes, keep warm for 5-15 minutes, and then degas to obtain the hot melt adhesive film intermediate; In step S3, the premixed intermediate is further heated to 130–140°C. This maintains the melt in a fully molten state and stabilizes the interface regulating components distributed in the amorphous regions and near phase boundaries. At this point, the added crystallization-inducing component achieves a more uniform dispersion in the melt. The crystallization-inducing component refers to a functional component that influences the initiation position, density, and distribution of crystal regions in the copolyamide. Its main function is to regulate the spatial distribution of crystal formation, rather than simply increasing the crystallization rate. Through a dispersion process lasting 15–35 minutes, the crystallization-inducing component gradually penetrates the premixed intermediate and forms smaller, more uniformly distributed induction centers in the melt. Maintaining a compatible boundary with the copolyamide matrix, it guides the preferential formation of crystal regions within specific micro-regions during subsequent cooling, resulting in a more refined and continuous supporting structure.

[0022] After dispersion, continue holding at a high temperature for 5–15 minutes. This helps the induction centers stabilize further within the melt and allows for the redistribution of various chain segments in the premixed intermediate under high-temperature conditions. This creates a more consistent starting state for the flow orientation and crystallization evolution during the next film formation process. Subsequently, degassing is performed to remove air bubbles, volatile small molecules, and locally trapped gases that were carried into the system during mixing and dispersion. This prevents these defects from transforming into voids, weak areas, or stress concentration points during extrusion film formation, thus obtaining a modified melt with both a controllable crystallization initiation base and a low level of internal defects.

[0023] S4: The hot melt adhesive film intermediate is extruded at 120-170°C to form a continuous film preform, and then heat-treated and re-formed in sequence. After cooling, a copolyamide hot melt adhesive film for power batteries is obtained.

[0024] In step S4, under the condition that the hot melt adhesive film intermediate already has a low defect level and a relatively clear crystallization initiation basis, the material is transformed from a molten state into a continuous film material, and the microstructure potential established in the previous steps is further implemented into the actual film. First, the hot melt adhesive film intermediate is transported to the extrusion film forming unit, maintaining a continuous and stable melt flow state within the range of 120–170°C, allowing it to smoothly pass through the die to form a continuous film preform. The continuous film preform is an initial film material with continuous thickness and a basically intact surface; its formation quality directly affects the effectiveness of heat treatment. During extrusion, the melt undergoes a controlled flow path and shear distribution, enabling the already formed crystallization induction centers to be more uniformly distributed in the film thickness direction, while further reducing residual microbubbles and localized concentrated areas, thus giving the film preform a more consistent thickness base and a more uniform internal structure after demolding. The resulting continuous film preform is in a pre-crystallization state, meaning the chain segments still retain a certain degree of mobility and can still undergo structural reorganization using thermal history. Furthermore, after the continuous preform is formed, heat treatment and refining are performed sequentially to further stabilize the internal structure and external dimensional state of the membrane. Heat treatment involves applying a controlled temperature process to the preform, allowing the pre-existing crystallization induction centers within the membrane to gradually function and guiding the copolyamide segments to form a more uniform distribution of crystalline and amorphous regions. This results in a more harmonious microstructure between the surface and interior of the membrane, reducing stress concentration caused by excessively rapid local crystallization or uneven shrinkage. Refining refers to morphological adjustments to the membrane material under low tension or constant traction conditions. This releases residual orientation stress from extrusion and heat treatment, and improves the smoothness, edge condition, and winding stability of the membrane material.

[0025] After the aforementioned continuous processes, the film gradually completes its shaping during the cooling stage, forming a finished hot melt adhesive film with good dimensional retention and thickness stability. In the bonding or encapsulation process of power batteries, the copolyamide hot melt adhesive film of this embodiment can both reactivate the surface contact capability when heated and maintain a relatively continuous internal support network after cooling. Therefore, under long-term pressure and temperature fluctuation conditions, it is more conducive to slowing down the accumulation of deformation and maintaining the stability of the interface support state.

[0026] In another embodiment, referring to Table 1, a comparative example is selected for performance testing.

[0027] Example 1 describes a copolyamide hot melt adhesive film prepared using the method described in this invention. Comparative Example 1 describes a film prepared by direct melt extrusion of a single copolyamide resin. During the preparation process, no two-stage responsive base resin construction, interface conditioning components, or crystallization inducing components are added. The film is made with basic film-forming ability by adjusting the melting temperature. Comparative Example 2 describes a film prepared by directly blending a copolyamide base resin with an interface conditioning component. Although interface adaptation treatment is performed during the preparation process, no crystallization inducing components are added, and no heat treatment or reshaping is performed on the internal structure of the film.

[0028] To ensure the comparability of test results, all samples were prepared as hot melt adhesive films with a thickness of 0.100 mm ± 0.005 mm and cut into specimens of the same specifications. The bonding substrate was uniformly selected as the aluminum sheet / insulating PET composite interface commonly used in power batteries. The hot pressing conditions were uniformly controlled at 125℃, 0.35 MPa, and 90 s. After pressing, the samples were placed in an environment of 23℃ and 50%RH for 24 hours before performance testing. Among them, the 180° peel strength was used to evaluate the interfacial bonding ability, the 85℃ / 0.50 MPa / 24h compression creep was used to evaluate the degree of slow deformation accumulation of the adhesive film under thermo-compression coupling conditions, the thickness retention rate after thermal cycling was used to evaluate the structural stability of the adhesive film after 10 cycles from -20℃ to 85℃, and the 85℃ shear retention rate was used to evaluate the support continuity of the adhesive film under high temperature load conditions.

[0029] As can be seen from the table, Example 1 outperforms both comparative examples in all four indicators, especially in terms of compression creep and thickness retention after thermal cycling. This indicates that Example 1, through the construction of the front-end base resin system, provides the material with a better flow and spreading foundation during the heating and bonding stage. Furthermore, the interface conditioning process improves the contact uniformity between the melt and the bonded interface. Additionally, the crystallization induction and subsequent heat treatment and refining processes create a more stable and continuous support structure within the membrane. Therefore, it is less prone to thickness decay, localized stress migration, and structural relaxation under continuous pressure and temperature fluctuations. In contrast, while Comparative Example 1 achieves basic bonding, its weaker internal support structure makes it more susceptible to deformation accumulation under high-temperature compression. Although Comparative Example 2 shows improved interface bonding compared to Comparative Example 1, the lack of subsequent crystallization structure refinement and membrane thermal history control means that its dimensional retention and support stability under long-term pressure and thermal cycling conditions are still inferior to Example 1. These test results demonstrate that the embodiments of the present invention not only perform well in terms of initial bonding performance, but also have a more significant advantage in terms of long-term service stability, which is of greater concern to power batteries.

[0030] Table 1: In one embodiment, step S1 includes: The copolyamide base resin is placed in a reaction vessel and heated to 90-110°C under a nitrogen atmosphere, and kept at the temperature for 20-30 minutes to obtain a molten copolyamide base resin. The copolyamide base resin, kept in a molten state, is kept at 90–120°C, and the stirring speed is adjusted to 150–300 rpm for continuous homogenization treatment for 20–40 minutes to obtain a base melt with a two-stage response characteristic. This two-stage response characteristic refers to maintaining flowable wetting ability during the heating stage and forming cohesive support ability during the cooling stage.

[0031] In the above embodiments, the copolyamide base resin was added to a reactor and slowly heated to 90–110°C under nitrogen protection, gradually transforming the resin from granular or blocky particles into a continuous melt. The nitrogen environment reduces the influence of air and moisture on the resin end groups during heating, making the melt state more stable and less prone to local viscosity fluctuations during subsequent homogenization. After holding at the temperature for 20–30 minutes, the incompletely melted particles inside the system basically disappeared, and a continuous molten phase formed in the reactor. At this point, the temperature was maintained within the range of 90–120°C, and the stirring speed was controlled at 150–300 rpm, allowing the molten resin to continuously tumble and exchange positions under controlled shear. After 20–40 minutes of homogenization, the copolyamides with different chain segment structures formed a more uniform distribution in the melt, alleviating the problem of inconsistent local melting rates, and the overall viscosity and softening range of the system tended to stabilize. The resulting base melt maintains a relatively stable flow state during subsequent heating and mixing. It spreads easily during heating and gradually builds cohesive strength during cooling, making it suitable as a unified matrix for introducing interface modifiers. The functional components added in the next step spread more evenly throughout the melt, avoiding localized enrichment or interfacial discontinuities during subsequent film formation.

[0032] In one example, in step S1, the copolyamide base resin includes at least two copolyamide resins with different crystallization tendencies and molecular weight distributions, including aliphatic copolyamides, semi-aromatic copolyamides, amino-terminated copolyamides, and carboxyl-terminated copolyamides.

[0033] In the above embodiments, the base resin is a combination of at least two copolyamide resins with different crystallization tendencies and molecular weight distributions, so that the material has different functions in the processing and use stages. Aliphatic copolyamides have better molecular chain flexibility, making it easier to form a flowable melt after heating, which is beneficial for wetting the surfaces to be bonded during hot pressing; semi-aromatic copolyamides have stronger chain segments, which helps maintain dimensional stability and high-temperature support capacity after cooling; amino-terminated and carboxyl-terminated copolyamides can improve the internal polar environment of the system, making it easier for subsequently added interface conditioning components to distribute to suitable locations, and also facilitating a more stable melt compatibility state between different resin components. The differences in crystallization rate and molecular weight distribution of the above copolyamide resins, when combined, can broaden the melt processing window, preventing the melt from becoming unstable too quickly during heating and gradually establishing a support network during cooling. This basic system takes into account both the spreading ability during the hot pressing stage and the structural retention ability after film formation, providing a more suitable material basis for interface adjustment, crystallization induction and thermal history treatment in subsequent steps, and making it easier for the final hot melt adhesive film to maintain its thickness and support state under the long-term pressure conditions of the power battery.

[0034] In one instance, step S2 includes: Under an inert atmosphere, the base melt is kept at 100-120°C, the interface conditioning component is added, the stirring speed is adjusted to 200-400 rpm, and the mixture is stirred for 10-20 minutes to obtain the first mixture; Heat the first mixture to 120-130°C, add the flow conditioning component, and continue stirring for 5-15 minutes while maintaining the speed to obtain the second mixture; Adjust the stirring speed to 150 rpm, and degas the second mixture under a vacuum of -0.04 to -0.09 MPa for 5 to 15 minutes to obtain a premixed intermediate.

[0035] In the above embodiments, after the basic melt has been formed, it is first stabilized at 100–120°C, and then an interface conditioning component is added. Utilizing the suitable melt viscosity at this temperature range, the component preferentially enters the amorphous regions and segmental junction regions of the copolyamide melt. At this point, the stirring speed is controlled at 200–400 rpm, balancing dispersion efficiency and melt stability, allowing the interface conditioning component to initially spread within 10–20 minutes, forming the first mixture. The system is then heated to 120–130°C, and a flow conditioning component is added. This temperature range is more conducive to further fine-tuning of the melt rheological state, enabling the system to maintain continuity while possessing flow characteristics more suitable for subsequent transport, dispersion, and film formation. After maintaining the original stirring speed and continuing to stir for 5–15 minutes, the interface conditioning and flow conditioning effects gradually superimpose in the same melt, forming the second mixture.

[0036] Reducing the stirring speed to 150 rpm and performing vacuum degassing, with the vacuum level controlled at -0.04 to -0.09 MPa, for 5 to 15 minutes, removes microbubbles, entrained air, and small amounts of volatile components introduced during the heating and mixing process. The resulting premixed intermediate is more stable when subsequently heated to higher temperatures, less prone to forming localized voids or weak zones before extrusion, and exhibits a more uniform interfacial layer, facilitating the formation of continuous support zones.

[0037] In one example, in step S2, the interface conditioning component includes at least one of anhydride-grafted polymer, polyimide-modified resin, and amide-containing block copolymer, and the flow conditioning component includes at least one of fatty acid amide, hydroxy fatty acid ester, and long-chain fatty acid glyceride.

[0038] In the above embodiments, the interface conditioning component and the flow conditioning component play the roles of interface adaptation and rheological finishing, respectively, in the premixing stage. The anhydride-grafted polymer, with its strong polar groups, improves the material's contact affinity with metal parts, insulating sheets, and composite interfaces after entering the copolyamide melt. The polyimide-modified resin combines heat resistance with a certain polar structure, enhancing interface stability without significantly weakening subsequent support capabilities. The amide-containing block copolymer helps to mitigate the transition between different polar regions. The fatty acid amides, hydroxy fatty acid esters, and long-chain fatty acid glycerides in the flow conditioning component primarily refine the melt flow state, ensuring continuous flow during mixing, transport, and film formation without affecting spreading and venting due to locally high viscosity. Through the combination of these components, the premixed intermediate more easily maintains a uniform melt state during the high-temperature dispersion stage, and the contact conditions with typical bonded interfaces of power batteries are more stable, thus creating a better foundation for the next step of introducing crystallization induction centers and forming an ordered microstructure.

[0039] In one instance, step S3 includes: Under an inert atmosphere, the premixed intermediate was kept at 130–140°C for 5–10 minutes. The crystallization inducing component was added, and the stirring speed was adjusted to 300–800 rpm. The mixture was dispersed for 10–20 minutes to obtain the mixed intermediate. Add at least one of heat-resistant oligomers or surface-modified microparticles to the mixed intermediate, increase the stirring speed to 600-1000 rpm, and continue to disperse for 5-15 minutes to form a mixture; The mixture is kept at 130-140℃ for 5-15 minutes and then degassed for 5-10 minutes under a vacuum of -0.03 to -0.08 MPa to obtain a hot melt adhesive film intermediate.

[0040] In the above embodiments, after the premixed intermediate enters the next stage, it is first kept at 130-140°C for 5-10 minutes to ensure that the internal temperature of the system is uniform, allowing the interface conditioning component and the flow conditioning component to further balance in the melt, while keeping the melt in a sufficiently activated state to facilitate the rapid entry of the subsequent inducing component into the system. The crystallization inducing component is then added, and the stirring speed is controlled at 300-800 rpm for 10-20 minutes. The shearing action formed at this time can uniformly bring the inducing centers into the interior of the melt, distributing them at key locations where crystal regions may form later. After obtaining the mixed intermediate, at least one of a heat-resistant oligomer or surface-modified microparticles is added, and the stirring speed is increased to 600-1000 rpm for further dispersion for 5-15 minutes. This utilizes higher shear force to break up any possible micro-agglomerates and also helps to stably embed the heat-resistant support unit or microparticles into the original melt network. The mixture is then held at 130–140°C for 5–15 minutes to further stabilize the distribution of each component in the melt and to make the chain segment arrangement and nucleation initiation conditions more consistent. Finally, vacuum degassing is performed to remove the air and a small amount of low-molecular-weight volatiles introduced during the high-shear dispersion process, resulting in a hot melt adhesive film intermediate with fewer defects and a more defined crystallization initiation basis.

[0041] In one embodiment, in step S3, the crystallization inducing component is an organic nucleating agent, which includes at least one of amide nucleating agents, aromatic carboxylate nucleating agents, and heterocyclic crystallization promoters; the heat-resistant oligomer includes at least one of polyimide oligomers, polyarylate oligomers, and aromatic polyamide oligomers; and the surface-modified inorganic particles include at least one of silica, talc, and alumina that have been surface-treated with silane coupling agents, titanate coupling agents, or aluminate coupling agents.

[0042] In the above embodiments, amide-based nucleating agents in the organic nucleating agents maintain good compatibility with the copolyamide matrix, and their dispersion facilitates the formation of refined crystallization initiation points; aromatic carboxylate nucleating agents improve the uniformity of crystal region formation; and heterocyclic crystallization promoters help stabilize the crystallization initiation process. The polyimide oligomers, polyarylate oligomers, and aromatic polyamide oligomers in the heat-resistant oligomers primarily provide heat-resistant support microregions within the film, ensuring good structural integrity of the material under subsequent heating or long-term pressure conditions. The surface-modified inorganic microparticles, using silica, talc, and alumina treated with silane coupling agents, titanate coupling agents, or aluminate coupling agents, aim to enhance the bonding between the inorganic phase and the organic melt, reduce particle agglomeration, and allow the microparticles to provide more stable microscale support within the system.

[0043] By combining the above three types of materials, the melt can form a more continuous support network and a more uniform internal structure after film formation, which significantly helps with dimensional stability and creep resistance.

[0044] In one embodiment, step S4 includes: The hot melt adhesive film intermediate is fed into an extrusion film forming device and extruded and cast at 120-170°C to form a continuous film preform. The continuous film preform is subjected to a first heat treatment at 80-120℃ for 5-8 minutes, and then the temperature is raised to 120-140℃ for a second heat treatment of 5-10 minutes. The continuous film preform, after its second heat treatment, is subjected to low-tension rewinding, cooled to room temperature, and then surface stabilization treatment to obtain a copolyamide hot melt adhesive film for power batteries.

[0045] In the above embodiments, after the hot melt adhesive film intermediate is introduced into the extrusion film forming device, it is extruded and cast in the range of 120 to 170°C. At this time, the melt has both a relatively stable flow state and a clear crystallization initiation basis, so it can form a continuous and flat initial film layer when passing through the die.

[0046] The continuous film preform obtained by casting is still in a state that can be further processed. A first heat treatment of 80–120℃ for 5–8 minutes is performed to allow for a gentle redistribution of the internal chain segments, initially releasing the localized orientation stress formed during extrusion and simultaneously balancing the early crystallization state. A second heat treatment of 120–140℃ for 5–10 minutes is then performed. This stage is closer to the structurally stable temperature range during subsequent use, further fixing the microstructure established in the previous stage and making the microstructure of the surface and central regions more harmonious.

[0047] After undergoing two heat treatments, the preform is then subjected to low-tension rewinding, which eliminates residual warping and edge stress under gentler traction conditions, resulting in a membrane material that is more suitable for industrial use in terms of flatness, dimensional consistency, and winding stability. Cooling to room temperature followed by surface stabilization treatment adjusts the microscopic contact state of the membrane surface, reduces self-adhesion tendencies during storage and die-cutting, and maintains reactivation capabilities for subsequent hot-pressing. The resulting hot melt adhesive film maintains its thickness more stably, supports the interface, and inhibits slow deformation accumulation under power battery assembly and long-term service conditions.

[0048] The present invention also proposes a copolyamide hot melt adhesive film for power batteries, which is prepared by any of the above-described methods for preparing a copolyamide hot melt adhesive film for power batteries.

[0049] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a copolyamide hot melt adhesive film for power batteries, characterized in that, include: S1: Take the copolyamide base resin and heat it to 90-120°C under an inert atmosphere to melt it. In the molten state, homogenize it to form a base melt. The base melt has a two-stage response characteristic. S2: Heat the base melt to 120-130°C, add the interface conditioning component and stir to obtain a premixed intermediate; S3: Heat the premixed intermediate to 130-140°C, add the crystallization induction component, disperse for 15-35 minutes, keep warm for 5-15 minutes, and then degas to obtain the hot melt adhesive film intermediate; S4: The hot melt adhesive film intermediate is extruded at 120-170°C to form a continuous film preform, and then heat-treated and re-formed in sequence. After cooling, a copolyamide hot melt adhesive film for power batteries is obtained.

2. The method for preparing a copolyamide hot melt adhesive film for power batteries according to claim 1, characterized in that, Step S1 includes: The copolyamide base resin is placed in a reaction vessel and heated to 90-110°C under a nitrogen atmosphere, and kept at the temperature for 20-30 minutes to obtain a molten copolyamide base resin. The copolyamide base resin is kept in a molten state at 90-120°C, and the stirring speed is adjusted to 150-300 rpm. The mixture is continuously stirred for 20-40 minutes to homogenize it, resulting in a base melt with a two-stage response characteristic. The two-stage response characteristic is that the base melt maintains flowable wetting ability during the heating stage and forms cohesive support ability during the cooling stage.

3. The method for preparing a copolyamide hot melt adhesive film for power batteries according to claim 1, characterized in that, In step S1, the copolyamide base resin includes at least two copolyamide resins with different crystallization tendencies and molecular weight distributions. The copolyamide resins include aliphatic copolyamides, semi-aromatic copolyamides, amino-terminated copolyamides, and carboxyl-terminated copolyamides.

4. The method for preparing a copolyamide hot melt adhesive film for power batteries according to claim 1, characterized in that, Step S2 includes: Under an inert atmosphere, the base melt is kept at 100-120°C, the interface conditioning component is added, the stirring speed is adjusted to 200-400 rpm, and the mixture is stirred for 10-20 minutes to obtain the first mixture; Heat the first mixture to 120-130°C, add the flow conditioning component, and continue stirring for 5-15 minutes while maintaining the speed to obtain the second mixture; Adjust the stirring speed to 150 rpm, and degas the second mixture under a vacuum of -0.04 to -0.09 MPa for 5 to 15 minutes to obtain a premixed intermediate.

5. The method for preparing a copolyamide hot melt adhesive film for power batteries according to claim 4, characterized in that, In step S2, the interface conditioning component includes at least one of anhydride grafted polymer, polyimide modified resin and amide-containing block copolymer, and the flow conditioning component includes at least one of fatty acid amide, hydroxy fatty acid ester and long-chain fatty acid glyceride.

6. The method for preparing a copolyamide hot melt adhesive film for power batteries according to claim 1, characterized in that, Step S3 includes: Under an inert atmosphere, the premixed intermediate was kept at 130–140°C for 5–10 minutes. The crystallization inducing component was added, and the stirring speed was adjusted to 300–800 rpm. The mixture was dispersed for 10–20 minutes to obtain the mixed intermediate. Add at least one of heat-resistant oligomers or surface-modified microparticles to the mixed intermediate, increase the stirring speed to 600-1000 rpm, and continue to disperse for 5-15 minutes to form a mixture; The mixture is kept at 130-140℃ for 5-15 minutes and then degassed for 5-10 minutes under a vacuum of -0.03 to -0.08 MPa to obtain a hot melt adhesive film intermediate.

7. The method for preparing a copolyamide hot melt adhesive film for power batteries according to claim 6, characterized in that, In step S3, the crystallization inducing component is an organic nucleating agent, which includes at least one of amide nucleating agents, aromatic carboxylate nucleating agents, and heterocyclic crystallization promoters; the heat-resistant oligomer includes at least one of polyimide oligomers, polyarylate oligomers, and aromatic polyamide oligomers; and the surface-modified inorganic particles include at least one of silica, talc, and alumina that have been surface-treated with silane coupling agents, titanate coupling agents, or aluminate coupling agents.

8. The method for preparing a copolyamide hot melt adhesive film for power batteries according to claim 1, characterized in that, Step S4 includes: The hot melt adhesive film intermediate is fed into an extrusion film forming device and extruded and cast at 120-170°C to form a continuous film preform. The continuous film preform is subjected to a first heat treatment at 80-120℃ for 5-8 minutes, and then the temperature is raised to 120-140℃ for a second heat treatment of 5-10 minutes. The continuous film preform after the second heat treatment is subjected to low-tension re-conditioning, cooled to room temperature, and surface stabilization treatment to obtain a copolyamide hot melt adhesive film for power batteries.

9. A copolyamide hot melt adhesive film for power batteries, characterized in that, The film is prepared by the method described in any one of claims 1-8 for a copolyamide hot melt adhesive film for power batteries.

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