Gradient curing process of hot melt adhesive layer and application thereof in composite shielding tape

Abstract

The application discloses a hot melt adhesive layer gradient curing process and application thereof in composite shielding tapes. The process comprises: preparing hot melt adhesive granules comprising EVA, POE, TPU and conductive fillers; coating the hot melt adhesive granules on the surface of a metal foil layer or a substrate layer after heating and melting to form a hot melt adhesive layer; hot-pressing the metal foil layer coated with the hot melt adhesive layer and the substrate layer, and sequentially passing through a first zone at 180-200 DEG C, a second zone at 140-160 DEG C and a third zone at 80-100 DEG C for gradient curing, and finally cooling to obtain a composite shielding tape. The hot melt adhesive adopts an EVA / POE / TPU ternary blending system, and the conductive fillers adopt a synergistic compounding system of conductive carbon black and nano silver wires. The application can take into account full penetration of the adhesive layer, interface chemical bonding, stable construction of the conductive network and internal stress release, and is suitable for the manufacture of composite shielding tapes in new energy automobile battery packs, liquid cooling systems, 5G communication equipment and high-temperature industrial environments.

Description

Technical Field

[0001] This invention relates to the field of composite shielding material manufacturing technology, and in particular to a hot melt adhesive layer gradient curing process and its application in composite shielding tape. Background Technology

[0002] Composite shielding tape is typically formed by combining a metal foil layer, an adhesive layer, and a substrate layer. It is widely used in electromagnetic shielding of wires and cables, insulation protection of battery packs in new energy vehicles, protection of peripheral structures in liquid cooling systems, and electromagnetic compatibility (EMC) applications of electronic equipment. With the development of new energy vehicles, 5G communications, and high-power electronic devices, composite shielding tape not only needs to possess good shielding performance but also needs to maintain stable adhesive strength and structural integrity under complex conditions such as high and low temperatures, immersion in liquid cooling media, and mechanical vibration.

[0003] In existing technologies, composite shielding tapes are typically made by applying hot melt adhesive and then hot-pressing it with metal foil or substrate, and curing it through a single temperature condition or a simple heat-cooling process. However, traditional isothermal curing processes have several problems in practical applications: First, when the adhesive layer is too fluid at high temperatures, it is easy to cause adhesive overflow or uneven thickness at the interface, while at lower temperatures it is difficult to fully penetrate into the microstructure of the metal foil and substrate surface; second, the thermal expansion coefficients of metal materials and polymer substrates differ greatly, and large residual stress is easy to accumulate inside the adhesive layer during the curing process, which can easily cause interface cracking and delamination during subsequent thermal cycling; third, for hot melt adhesive systems containing conductive fillers, traditional curing methods may also lead to uneven distribution or local agglomeration of conductive fillers, thereby affecting the stability of shielding performance.

[0004] Furthermore, existing common single-EVA, single-POE, or single-TPU adhesive systems typically struggle to simultaneously achieve optimal bond strength, liquid cooling resistance, high-temperature resistance, low-temperature flexibility, and conductive network stability. Therefore, achieving a comprehensive improvement in interfacial bonding, conductivity, and environmental adaptability of composite shielding tapes through a combination of hot melt adhesive formulation design and curing process control has become a crucial technical challenge in this field. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a hot melt adhesive layer gradient curing process for manufacturing composite shielding tapes that balances sufficient adhesive layer penetration, interfacial chemical bonding, stable construction of conductive networks, and internal stress release. This process is suitable for use in the manufacture of composite shielding tapes in new energy vehicle battery packs, liquid cooling systems, 5G communication equipment, and high-temperature industrial environments, and its application in composite shielding tapes.

[0006] The technical solution adopted in this invention is: a gradient curing process for a hot melt adhesive layer, used to laminate a hot melt adhesive layer between a metal foil layer and a substrate layer, the process comprising the following steps: S1. Prepare hot melt adhesive granules, wherein the hot melt adhesive granules include EVA, POE, TPU and conductive fillers; S2. The hot melt adhesive granules are heated and melted, and then coated onto the surface of the metal foil layer or the surface of the substrate layer to form a hot melt adhesive layer; S3. The metal foil layer coated with hot melt adhesive is hot-pressed together with the substrate layer, and the composite structure is sequentially cured through the first zone, the second zone and the third zone. The temperature of the first zone is 180-200℃, which is used to fully melt and penetrate the hot melt adhesive layer. The temperature of the second zone is 140-160℃, which is used to control the flow of the hot melt adhesive layer and promote interfacial chemical bonding; The temperature of the third zone is 80-100℃, which is used to slowly cool the hot melt adhesive layer and release internal stress. S4. After cooling, the material is wound up or cut to obtain the composite shielding tape.

[0007] A further improvement to the above scheme is that the EVA, POE and TPU in the hot melt adhesive granules constitute a ternary blend system, which, by mass parts, includes: 30-60 parts of EVA, 15-35 parts of POE and 15-40 parts of TPU.

[0008] A further improvement to the above scheme is that the vinyl acetate content of the EVA is 18%-28%, and the melt index is 5-40 g / 10 min; The POE has an octene content of 20%-40% and a melt index of 1-15 g / 10 min; The TPU is a polyester-type TPU or a polyether-type TPU with a Shore hardness of 70A-90A.

[0009] A further improvement to the above scheme is that the conductive filler includes conductive carbon black and silver nanowires; The amount of conductive carbon black added accounts for 5%-15% of the total mass of the hot melt adhesive granules, and the amount of silver nanowires added accounts for 0.5%-5% of the total mass of the hot melt adhesive granules.

[0010] A further improvement to the above scheme is that the conductive carbon black has a DBP oil absorption value of not less than 300mL / 100g and a specific surface area of ​​not less than 600m² / g. The diameter of the silver nanowires is 30-80 nm, and the aspect ratio is 100-1000.

[0011] A further improvement to the above scheme is that the hot melt adhesive granules also include tackifying resin, antioxidant and silane coupling agent; The amount of the tackifying resin added is 3-10 parts, the amount of the antioxidant added is 0.5-2 parts, and the amount of the silane coupling agent added is 0.5-2 parts.

[0012] A further improvement to the above scheme is that step S1 includes: S11. Add EVA, POE and TPU to a high-speed mixer and mix. S12. Premix conductive carbon black, silver nanowires and additives; S13. The mixed resin particles, premixed conductive filler and additives are added to a twin-screw extruder for melt blending, and then pelletized to obtain the hot melt adhesive granules.

[0013] A further improvement to the above scheme is that the temperature of the twin-screw extruder is 160-200℃ and the screw speed is 200-400rpm.

[0014] A further improvement to the above scheme is that, in step S2, the coating temperature of the hot melt adhesive layer is 180-200℃, the coating thickness is 30-150μm, and the dry film thickness is 20-100μm.

[0015] A further improvement to the above scheme is that, in step S3, the residence time in the first zone is 5-30 seconds, and the combined pressure is 0.2-0.8 MPa; The dwell time in the second zone is 15-60 seconds, and the pressure is 0.1-0.3 MPa; The dwell time in the third zone is 30-120 seconds, and the cooling rate is 0.5-5℃ / second.

[0016] A further improvement to the above scheme is that the dwell time in the first area is 10-20 seconds; The dwell time in the second zone is 20-40 seconds; The dwell time in the third zone is 45-90 seconds; The cooling rate is 1-3℃ / second.

[0017] A further improvement to the above scheme is that a smooth temperature gradient is adopted between the first, second and third zones, and the temperature change rate is controlled at 5-15℃ / second.

[0018] A further improvement to the above scheme is that the first zone, the second zone, and the third zone are achieved through a multi-segment independently temperature-controlled heating roller system, or through a segmented heating tunnel furnace.

[0019] A further improvement to the above scheme is that, after step S4, a curing process is added: the obtained composite shielding tape is placed in an environment of 40-60℃ for 24-72 hours.

[0020] A composite shielding tape prepared by a hot melt adhesive layer gradient curing process includes a metal foil layer, a substrate layer, and a hot melt adhesive layer located between the metal foil layer and the substrate layer. The hot melt adhesive layer is an EVA / POE / TPU ternary blend system, and contains a conductive filler system composed of conductive carbon black and silver nanowires.

[0021] A further improvement to the above scheme is that the metal foil layer is an aluminum foil layer or a copper foil layer.

[0022] A further improvement to the above scheme is that the substrate layer is a PET film layer or a polyimide film layer.

[0023] A further improvement to the above scheme is that the hot melt adhesive layer and the metal foil layer have a physical interlocking structure and a chemical bonding interface, and a conductive network composed of conductive carbon black and silver nanowires is formed inside the hot melt adhesive layer.

[0024] The beneficial effects of this invention are: Compared with the prior art, the present invention uses a three-zone gradient temperature field to cure the hot melt adhesive layer. In the first zone, a higher temperature is used to fully melt the hot melt adhesive layer and penetrate into the microstructure of the metal foil layer and the substrate layer. In the second zone, the flow of the adhesive layer is controlled and the polar groups are chemically bonded to the metal surface. In the third zone, internal stress is released by slow cooling, thereby simultaneously taking into account interfacial penetration, interfacial reaction and curing stability.

[0025] This invention establishes a dual bonding mechanism between the hot melt adhesive layer and the metal foil layer by forming a physical interlocking structure in the high-temperature zone and a chemical bonding interface in the medium-temperature zone. This effectively improves peel strength and reduces the risk of delamination under temperature cycling and mechanical vibration conditions.

[0026] This invention employs a conductive filler system that synergistically combines conductive carbon black and silver nanowires. The conductive carbon black forms the basic conductive contact points, while the silver nanowires bridge the carbon black aggregates, enabling the formation of a stable three-dimensional conductive network with a relatively low total filler content. Furthermore, the gradient curing process facilitates the uniform distribution and stable locking of the conductive network within the adhesive layer, thereby improving the conductivity and shielding effectiveness stability of the composite shielding tape.

[0027] This invention employs a ternary blend system of EVA / POE / TPU, in which EVA provides good adhesion and processability, POE improves flexibility and low-temperature crack resistance, and TPU enhances chemical resistance, temperature resistance, and high-temperature bonding strength, thereby making the composite shielding tape more suitable for liquid cooling systems in new energy vehicles, high-temperature equipment, and wide-temperature-range application environments.

[0028] The hot melt adhesive granule preparation, coating, gradient curing and post-treatment steps of this invention are logically clear, and the temperature, pressure, residence time and cooling rate parameter windows are well defined. They can be achieved through a multi-segment heating roller system or a segmented tunnel oven, and are therefore suitable for industrial continuous production.

[0029] By controlling the gradient temperature field and the slow cooling process, this invention can reduce the residual stress at the interface caused by the difference in the thermal expansion coefficients of different materials, thereby improving the structural stability and performance retention of the composite shielding strip under operating temperature conditions of -40℃ to 125℃ or even higher. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of a portion of the structure of the present invention; Figure 3 This is an enlarged schematic diagram of the bonding area of ​​the present invention; Figure 4 This is a schematic diagram of the gradient curing process of the hot melt adhesive layer of the present invention.

[0031] Explanation of reference numerals in the attached figures: Metal foil layer 1; Substrate layer 2; Hot melt adhesive layer 3; Physical occlusal structure 31; Chemical bonding interface 32; Conductive carbon black 41; Silver nanowires 42. Detailed Implementation

[0032] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0033] It should be noted that when a component is said to be "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0035] like Figures 1-4 As shown, this invention relates to a gradient curing process for a hot melt adhesive layer and its application in composite shielding tapes. This process is mainly used to stably bond a hot melt adhesive layer 3 between a metal foil layer 1 and a substrate layer 2, resulting in a composite shielding tape with high peel strength, good liquid cooling resistance, good high-temperature resistance, and stable conductive shielding effectiveness. To achieve the above objectives, this invention designs the composition system of the hot melt adhesive granules and precisely controls the curing process of the hot melt adhesive layer 3 through a three-zone gradient temperature field consisting of a first zone, a second zone, and a third zone. This improves upon problems such as uneven adhesive penetration, internal stress accumulation, and insufficient interfacial bonding present in traditional isothermal curing methods.

[0036] The composite shielding strip obtained by this invention includes a metal foil layer 1, a substrate layer 2, and a hot melt adhesive layer 3 located between the metal foil layer 1 and the substrate layer 2. The metal foil layer 1 can be an aluminum foil layer or a copper foil layer, providing the conductive shielding body required for electromagnetic shielding. The substrate layer 2 can be a PET film layer, a polyimide film layer, or other polymer film, providing mechanical support, insulation protection, and a flexible structural foundation. The hot melt adhesive layer 3, located between the metal foil layer 1 and the substrate layer 2, serves both as the adhesive between the two layers and as a conductive connection and stress buffer.

[0037] The key to this invention is that the hot melt adhesive layer 3 is not a simple ordinary adhesive layer, but adopts a special EVA / POE / TPU ternary blend system and is compounded with conductive fillers such as conductive carbon black 41 and nano silver wire 42. After curing, it can form a stable bond with the metal foil layer 1 and the substrate layer 2, and can also build a continuous conductive network inside the adhesive layer, which is conducive to forming a complete electromagnetic shielding path.

[0038] The hot melt adhesive granules of this invention comprise three main resins: EVA (ethylene-vinyl acetate copolymer), POE (polyolefin elastomer), and TPU (thermoplastic polyurethane elastomer), forming a ternary blend system. This ternary blending method leverages the complementary advantages of different resins. EVA, as the base resin, provides good adhesion and melt processing flowability. EVA contains vinyl acetate groups, which, being polar groups, are beneficial for improving the wettability and interfacial adhesion to the metal foil layer 1. In this invention, the vinyl acetate content of EVA is preferably 18%-28%, more preferably 22%-25%. If the vinyl acetate content is too low, the adhesive layer lacks polarity, resulting in decreased adhesion to the metal foil layer 1; if the vinyl acetate content is too high, thermal stability decreases. The melt index of EVA is preferably 5-40 g / 10 min, more preferably 10-25 g / 10 min, to balance coating flowability and film-forming stability.

[0039] POE is used to improve the flexibility, low-temperature crack resistance, and stress buffering capacity of the hot melt adhesive layer 3 during thermal cycling. The octene content of POE is preferably 20%-40%, and the melt index is preferably 1-15 g / 10 min, more preferably 3-8 g / 10 min. The introduction of POE can reduce the modulus of the adhesive layer, allowing it to maintain good flexibility and crack resistance even at low temperatures such as -40°C. It also helps absorb thermal stress caused by the difference in thermal expansion coefficients between the metal foil layer 1 and the substrate layer 2 during the use of the composite shielding tape.

[0040] TPU is a thermoplastic polyurethane elastomer used to improve the chemical resistance, high-temperature resistance, and interfacial high-temperature bonding strength of the hot melt adhesive layer 3. Polyester-type TPU is preferred, but polyether-type TPU can also be used. The urethane and ester bonds in TPU have strong polarity, which facilitates strong interaction with metal surfaces, thereby improving interfacial stability under high-temperature conditions. The Shore hardness of TPU can be 70A-90A. TPU can also improve the cohesive strength of the adhesive layer and enhance creep resistance, making the composite shielding tape less prone to adhesive layer flow failure under long-term high-temperature use.

[0041] In terms of specific proportions, the preferred ternary blend system by mass parts is: 30-60 parts EVA, 15-35 parts POE, and 15-40 parts TPU; more preferably, 40-50 parts EVA, 20-30 parts POE, and 20-30 parts TPU. Through the above proportion design, a good balance can be achieved between adhesion, flexibility, high-temperature resistance, and processability.

[0042] The conductive filler of this invention employs a synergistic compounding of conductive carbon black 41 and silver nanowires 42. The conductive carbon black 41 is a high-structure conductive carbon black, preferably with an oil absorption value of DBP (dibutyl phthalate) of not less than 300 mL / 100 g, more preferably 360-500 mL / 100 g; its specific surface area is preferably not less than 600 m² / g. High-structure conductive carbon black more readily forms a basic conductive contact network in the resin matrix.

[0043] The silver nanowires 42 preferably have a diameter of 30-80 nm, more preferably 40-60 nm, and an aspect ratio of 100-1000. Due to their one-dimensional high aspect ratio, the silver nanowires 42 can form bridging pathways between the conductive carbon black aggregates 41, thereby constructing a "point-line-point" three-dimensional conductive network. This synergistic structure can significantly reduce the total filler content required for the formation of the conductive network, avoiding the decrease in adhesive adhesion and flexibility caused by excessive addition of conductive carbon black when used alone.

[0044] Regarding the specific content, the amount of conductive carbon black 41 added is preferably 5%-15% of the total mass of the hot melt adhesive granules, more preferably 8%-12%; the amount of nano silver wire 42 added is preferably 0.5%-5% of the total mass of the hot melt adhesive granules, more preferably 1%-3%. Through this compounding method, a balance can be achieved between conductivity, adhesion and processability.

[0045] To further optimize the processing and interface properties of the hot melt adhesive layer 3, the hot melt adhesive granules of the present invention may also include tackifying resin, antioxidant and silane coupling agent.

[0046] The tackifying resin is preferably a rosin ester, C5 / C9 petroleum resin, or terpene phenolic resin, and its addition amount is 3-10 parts. The tackifying resin can improve the wetting ability and initial tack of the molten adhesive layer to the metal foil layer 1 and the substrate layer 2.

[0047] The preferred antioxidant is a blend of hindered phenols and phosphites, such as antioxidants 1010 and 168, added at a rate of 0.5-2 parts. The antioxidant is used to inhibit the thermo-oxidative degradation of the hot melt adhesive during melt blending and high-temperature coating.

[0048] The preferred silane coupling agent is KH-550, KH-560, etc., with an addition amount of 0.5-2 parts. During the subsequent medium-temperature curing window in the second zone, the silane coupling agent can participate in the condensation reaction on the metal surface to form Si-OM bonds, thereby improving the chemical bonding strength between the hot melt adhesive layer 3 and the metal foil layer 1.

[0049] In addition, in some high thermal conductivity scenarios, thermally conductive fillers such as boron nitride and alumina can be added, but these fillers are optional components and will not be discussed in this embodiment.

[0050] In this invention, the hot melt adhesive granules are preferably prepared by twin-screw melt blending. The specific steps are as follows: First, add EVA, POE, and TPU to a high-speed mixer at 1000-2000 rpm and mix for 3-5 minutes to ensure uniform premixing of the three resin particles. Then, premix conductive carbon black 41, silver nanowires 42, and powder additives such as tackifying resin, antioxidants, and silane coupling agents. To ensure more uniform dispersion of the silver nanowires 42, high-speed stirring or ball milling can be used to prevent significant entanglement or localized agglomeration of the silver nanowires 42 before they are added to the resin system.

[0051] Subsequently, the resin premix and powder additive premix are added together to a twin-screw extruder for melt blending. The temperature of the twin-screw extruder can be set to 160-200℃, gradually increasing from the feed section to the die head section; the screw speed can be set to 200-400 rpm. Through the dispersing and mixing effect of the twin screws, conductive carbon black 41 and nano-silver wires 42 can be distributed relatively uniformly in the ternary blend resin system, forming a preliminary conductive network structure. The blended melt is then subjected to underwater pelletizing or strand pelletizing to obtain hot melt adhesive granules.

[0052] Through the above preparation method, the conductive filler inside the hot melt adhesive granules can be dispersed more uniformly, creating conditions for further stabilizing the conductive network in the subsequent coating and gradient curing stages.

[0053] Hot melt adhesive granules are added to a hot melt adhesive coating apparatus and heated to melt. The coating temperature is preferably 180-200℃. The molten hot melt adhesive is evenly coated onto the surface of the metal foil layer 1 or the substrate layer 2 through a slit die or a comma-shaped doctor blade to form a hot melt adhesive layer 3. The wet film thickness of the hot melt adhesive layer 3 can be controlled to be 30-150μm, and the dry film thickness can be controlled to be 20-100μm.

[0054] When it is necessary to prioritize enhancing the interfacial interaction between the hot melt adhesive layer 3 and the metal foil layer 1, it is preferable to first apply the hot melt adhesive to the surface of the metal foil layer 1; when considering production line layout or other process conditions, it can also be first applied to the surface of the substrate layer 2. Regardless of the application method, in the subsequent lamination process, the hot melt adhesive layer 3 will undergo thermo-press bonding and gradient curing with the other layer material.

[0055] The core of this invention lies in the fact that when hot-pressing the metal foil layer 1 coated with hot melt adhesive layer 3 to the substrate layer 2, instead of using the traditional single-area isothermal curing, the metal foil layer 1 passes through a gradient temperature field formed by the first, second and third zones in sequence, thereby achieving different functions at different stages.

[0056] The temperature of the first zone is 180-200℃, preferably 185-195℃. In this zone, the hot melt adhesive layer 3 is in a molten state with low viscosity, which can fully wet and penetrate into the micro-nano uneven structure on the surface of the metal foil layer 1 and the micro-rough structure on the surface of the substrate layer 2 under the action of composite pressure, thereby forming the initial physical interlocking structure 31.

[0057] The composite pressure in the first zone is 0.2-0.8 MPa, preferably 0.3-0.5 MPa; the residence time is 5-30 seconds, preferably 10-20 seconds. If the residence time is too short, the hot melt adhesive layer 3 will not be fully penetrated; if the residence time is too long, it may lead to excessive flow of the adhesive layer or even local overflow. Therefore, in this invention, by controlling the temperature, pressure, and residence time, the hot melt adhesive layer 3 mainly performs the functions of "rapid melting - sufficient wetting - forming physical interlocking" in this stage.

[0058] The temperature in the second zone is 140-160℃, preferably 145-155℃. In this zone, the viscosity of the hot melt adhesive layer 3 is higher than that in the first zone, the flowability is controlled, and excessive flow no longer occurs. At the same time, the polar groups and silane coupling agents in the adhesive layer are in a more suitable reaction and orientation window.

[0059] Specifically, polar groups such as ester groups in EVA and urethane and ester bonds in TPU are more likely to align towards the surface of metal foil layer 1 under these temperature conditions, thereby enhancing interfacial molecular interactions. Simultaneously, the active groups in the silane coupling agent can undergo condensation reactions with hydroxyl groups on the metal surface, forming a chemically bonded interface 32. Thus, the hot melt adhesive layer 3 and the metal foil layer 1 not only exhibit physical interlocking but also further form chemical bonds.

[0060] The pressure in the second zone can be 0.1-0.3 MPa, and the residence time is 15-60 seconds, preferably 20-40 seconds. Since the goal of this stage is to promote interfacial reaction and stabilize the adhesive layer thickness, it is not necessary to maintain the same high composite pressure as in the first zone; a lower holding pressure is sufficient.

[0061] The temperature in the third zone is 80-100℃, preferably 85-95℃. The core function of this stage is to slowly cool the hot melt adhesive layer 3, gradually transforming it from a viscous flow state to a highly elastic state and then to a solid state. At the same time, it releases residual thermal stress at the interface and stably "freezes" the dispersion state of the conductive filler and the conductive network inside the adhesive layer.

[0062] The dwell time in the third zone is 30-120 seconds, preferably 45-90 seconds; the cooling rate is 0.5-5℃ / second, preferably 1-3℃ / second. By adopting a gentler cooling method, the thermal stress concentration in the hot melt adhesive layer 3 caused by the difference in thermal expansion coefficients between the metal foil layer 1 and the substrate layer 2 can be significantly reduced, thereby reducing the risk of interface cracking or delamination during subsequent use.

[0063] Meanwhile, since the conductive carbon black 41 and the silver nanowires 42 underwent redispersion and bridging adjustment at high and medium temperatures, the slow cooling of the third zone allowed its conductive network to remain stable, avoiding the problem of local filler network breakage or uneven distribution caused by rapid cooling.

[0064] A smooth temperature gradient is preferably used between the first, second, and third zones, with the temperature change rate controlled at 5-15℃ / second to avoid thermal shock caused by sudden temperature changes. This gradient temperature field can be achieved through a multi-segment independently temperature-controlled heating roller system or a segmented heating tunnel oven. When using a multi-segment heating roller system, three sets of independently temperature-controlled rollers can be sequentially arranged along the travel direction on the production line; when using a segmented tunnel oven, the composite structure travels sequentially through different temperature zones and completes curing.

[0065] After cooling in the third zone, the resulting composite structure can be directly wound up and then cut according to requirements to obtain the composite shielding tape. In a preferred embodiment, a curing treatment step can be added, in which the composite shielding tape is placed in an environment of 40-60℃ for 24-72 hours to further complete the subsequent reaction of the silane coupling agent and stabilize the interface structure, thereby further improving the peel strength and long-term stability.

[0066] If necessary, the substrate layer 2 can be subjected to corona treatment or plasma treatment before or after winding to further enhance the interfacial bonding between the substrate layer 2 and the hot melt adhesive layer 3.

[0067] Through the above process, the composite shielding tape obtained by the present invention can form a physical interlocking structure 31 and a chemical bonding interface 32 between the metal foil layer 1 and the hot melt adhesive layer 3. The physical interlocking structure 31 originates from the high-temperature penetration in the first region, and the chemical bonding interface 32 originates from the medium-temperature interface reaction in the second region. At the same time, a conductive network composed of conductive carbon black 41 and silver nanowires 42 is formed inside the hot melt adhesive layer 3.

[0068] The composite shielding tape has the following characteristics: Firstly, it has higher interfacial bonding strength, which can resist interfacial damage caused by high and low temperature cycling, mechanical vibration, and immersion in liquid cooling media; secondly, the internal conductive network of the hot melt adhesive layer 3 is more continuous and uniform, which can improve the stability of the electromagnetic shielding network; and thirdly, through the flexibility, temperature resistance, and liquid cooling resistance provided by the EVA / POE / TPU ternary blend system, the composite shielding tape is more suitable for applications in new energy vehicle battery packs, liquid cooling systems, 5G communication equipment, and high-temperature industrial environments.

[0069] In summary, this invention, through the design of a hot melt adhesive granule formulation system and the sequential penetration, reaction, and slow cooling curing of the hot melt adhesive layer 3 in a three-zone gradient temperature field, solves the problems of uneven adhesive penetration, high internal stress, insufficient interfacial bonding, and unstable conductive network in traditional composite shielding tape production. This solution improves both the peel strength and structural stability of the composite shielding tape, as well as its conductive shielding performance and environmental adaptability, demonstrating clear technical benefits and promising industrial application prospects.

[0070] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A gradient curing process for a hot melt adhesive layer, characterized in that, The process for laminating a hot melt adhesive layer between a metal foil layer and a substrate layer includes the following steps: S1. Prepare hot melt adhesive granules, wherein the hot melt adhesive granules include EVA, POE, TPU and conductive fillers; S2. The hot melt adhesive granules are heated and melted, and then coated onto the surface of the metal foil layer or the surface of the substrate layer to form a hot melt adhesive layer; S3. The metal foil layer coated with hot melt adhesive is hot-pressed together with the substrate layer, and the composite structure is sequentially cured through the first zone, the second zone and the third zone. The temperature of the first zone is 180-200℃, which is used to fully melt and penetrate the hot melt adhesive layer. The temperature of the second zone is 140-160℃, which is used to control the flow of the hot melt adhesive layer and promote interfacial chemical bonding; The temperature of the third zone is 80-100℃, which is used to slowly cool the hot melt adhesive layer and release internal stress. S4. After cooling, the material is wound up or cut to obtain the composite shielding tape.

2. The gradient curing process for hot melt adhesive layer according to claim 1, characterized in that: The EVA, POE and TPU in the hot melt adhesive granules constitute a ternary blend system, which, by mass parts, includes: 30-60 parts of EVA, 15-35 parts of POE and 15-40 parts of TPU.

3. The gradient curing process for the hot melt adhesive layer according to claim 2, characterized in that: The vinyl acetate content of the EVA is 18%-28%, and the melt index is 5-40 g / 10 min; The POE has an octene content of 20%-40% and a melt index of 1-15 g / 10 min; The TPU is a polyester-type TPU or a polyether-type TPU with a Shore hardness of 70A-90A.

4. The gradient curing process for hot melt adhesive layer according to claim 1, characterized in that: The conductive filler includes conductive carbon black and silver nanowires; The amount of conductive carbon black added accounts for 5%-15% of the total mass of the hot melt adhesive granules, and the amount of silver nanowires added accounts for 0.5%-5% of the total mass of the hot melt adhesive granules. The conductive carbon black has a DBP oil absorption value of not less than 300 mL / 100 g and a specific surface area of ​​not less than 600 m² / g. The diameter of the silver nanowires is 30-80 nm, and the aspect ratio is 100-1000.

5. The gradient curing process for hot melt adhesive layer according to claim 1, characterized in that: The hot melt adhesive granules also include tackifying resin, antioxidant and silane coupling agent; The amount of the tackifying resin added is 3-10 parts, the amount of the antioxidant added is 0.5-2 parts, and the amount of the silane coupling agent added is 0.5-2 parts.

6. The gradient curing process for hot melt adhesive layer according to claim 1, characterized in that: Step S1 includes: S11. Add EVA, POE and TPU to a high-speed mixer and mix. S12. Premix conductive carbon black, silver nanowires and additives; S13. The mixed resin particles, premixed conductive filler and additives are added to a twin-screw extruder for melt blending, and then pelletized to obtain the hot melt adhesive granules; The temperature of the twin-screw extruder is 160-200℃, and the screw speed is 200-400rpm.

7. The gradient curing process for hot melt adhesive layer according to claim 1, characterized in that: In step S2, the coating temperature of the hot melt adhesive layer is 180-200℃, the coating thickness is 30-150μm, and the dry film thickness is 20-100μm.

8. The gradient curing process for hot melt adhesive layer according to claim 1, characterized in that: In step S3, the residence time in the first zone is 5-30 seconds, and the combined pressure is 0.2-0.8 MPa. The dwell time in the second zone is 15-60 seconds, and the pressure is 0.1-0.3 MPa; The dwell time in the third zone is 30-120 seconds, and the cooling rate is 0.5-5℃ / second.

9. The gradient curing process for hot melt adhesive layers according to claim 1, characterized in that: After step S4, a curing process is also included: the obtained composite shielding tape is placed in an environment of 40-60°C for 24-72 hours.

10. A composite shielding tape prepared by the gradient curing process of the hot melt adhesive layer according to any one of claims 1-9, characterized in that, It includes a metal foil layer, a substrate layer, and a hot melt adhesive layer located between the metal foil layer and the substrate layer; the hot melt adhesive layer is an EVA / POE / TPU ternary blend system and contains a conductive filler system composed of conductive carbon black and silver nanowires; The metal foil layer is an aluminum foil layer or a copper foil layer; The substrate layer is a PET film layer or a polyimide film layer; The hot melt adhesive layer and the metal foil layer have a physical interlocking structure and a chemical bonding interface, and a conductive network composed of conductive carbon black and silver nanowires is formed inside the hot melt adhesive layer.

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