Composite hollow panel and method of manufacture

Abstract

The application discloses a kind of composite hollow plate and preparation method, belong to composite plate preparation technical field.Composite hollow plate includes outer plate and inner plate, and a plurality of corrugated support structures are connected between outer plate and inner plate, and adjacent corrugated support structures are cavity.Outer plate material is added wear-resistant reinforcing agent to improve surface wear resistance, and epoxy-amine binuclear double-wall microcapsule is introduced in inner plate material to enhance crack repair ability, and shape memory reinforcing agent is added in corrugated support structure material to give material shape memory characteristics.The application solves the technical problems that the strength and toughness of the existing composite hollow plate are difficult to consider, the service life is short, the cushioning performance is poor, and the interface bonding strength is insufficient, and is especially suitable for steel coil packaging and other application scenarios that require repeated use and high reliability.

Description

Technical Field

[0001] This invention relates to the field of composite material plate preparation technology, and provides a composite hollow plate and its preparation method. Background Technology

[0002] With the rapid development of the global steel industry and the increasing frequency of international trade, steel coils, as an important form of steel product, require reliable packaging materials for protection during production, storage, and transportation. Steel coil packaging materials not only need to withstand the enormous weight of the coils themselves, but also resist various impacts, vibrations, and compressive loads during loading, unloading, and long-distance transportation, while also preventing scratches and corrosion on the coil surface. Traditional steel coil packaging materials mainly include wooden pallets, metal frames, and simple plastic liners. These materials are either too heavy, increasing transportation costs, lack sufficient strength, are easily damaged, or fail to provide effective cushioning protection. Composite material packaging boards, with their high specific strength, high specific modulus, strong design flexibility, and corrosion resistance, are gradually becoming the ideal choice for steel coil packaging. In use, these packaging boards need to withstand the static pressure of the steel coils for extended periods, absorb various dynamic impacts during transportation, and be reusable multiple times to reduce packaging costs. However, existing packaging boards still face many technical bottlenecks in steel coil packaging applications.

[0003] Existing packaging panels generally use a single thermosetting resin system, which often presents a contradiction between strength and toughness. When the formulation design focuses on improving strength, the increased cross-linking density leads to increased brittleness, making the material prone to brittle fracture under impact loads and unable to effectively absorb impact energy. When the formulation design focuses on improving toughness, the decreased cross-linking density leads to a decrease in strength and stiffness, making it unable to withstand the weight load of the steel coil. This inherent contradiction between strength and toughness makes it difficult for existing composite hollow panels to simultaneously meet the dual requirements of high load-bearing capacity and high impact resistance for steel coil packaging. In addition, existing panel materials lack effective wear-resistant design, and the surface is easily worn under repeated contact and friction with the steel coil. The debris generated by wear not only contaminates the surface of the steel coil but also accelerates the deterioration of the material itself. Once damage cracks occur in existing composite hollow panels during use, they persist and continue to propagate under stress, eventually leading to material failure. Steel coil packaging materials inevitably suffer from various mechanical damages in actual use, such as bumps during loading and unloading, vibration fatigue during transportation, and stress concentration at the edges of the steel coil, all of which can generate microcracks within the material. Although these microcracks are initially very small or even invisible to the naked eye, they gradually connect and expand under cyclic loading to form macroscopic cracks, severely weakening the material's load-bearing capacity and service life. Current technologies lack active repair mechanisms for damaged cracks; once materials are damaged, they can only be repaired manually, which not only increases maintenance costs and downtime but also wastes resources. This is especially true for steel coil packaging materials that require repeated use, as the inability to repair accumulated damage severely limits their reuse frequency and economic efficiency. Existing packaging panels often use linear corrugated or grid structures for their support structures. These regular geometric structures are prone to stress concentration at turning points or intersections under stress, leading to premature local failure. The material in the stress concentration area yields or fractures first, while the strength of other areas is not fully utilized, resulting in low material utilization. The load-displacement curve of linear support structures during compression typically exhibits an approximately linear characteristic, lacking a clear energy absorption plateau region. This means that the material reaches its maximum load-bearing capacity with a small amount of deformation and then becomes unstable and fails, unable to continuously absorb energy over a large deformation range. This cushioning characteristic is detrimental to steel coil packaging applications because an ideal cushioning material should provide relatively stable buffering force over a large deformation stroke, thus gently absorbing impact energy rather than generating severe load peaks. In existing packaging panels, the interfacial bond strength between the panel and the core support structure is often insufficient during fabrication, making them prone to delamination failure under shear or peel loads. The interface is the weakest link in composite material structures, and the quality of the interfacial bond directly determines whether the multi-layer structure can collaboratively bear loads and achieve overall performance.In existing manufacturing processes, the resin does not sufficiently impregnate the fiber reinforcement, resulting in areas of dry fiber or insufficient resin content, particularly in the central region of the fiber bundle. This leads to a small contact area and fewer chemical bonding points between the fiber and the resin matrix. Mismatched shrinkage during curing of different layers also generates residual stress at the interface, further weakening the interfacial bond strength. When the composite hollow board is subjected to complex stress states during use, the weak interface cracks first and propagates rapidly, causing the panel to separate from the supporting structure, and the overall structure to lose its load-bearing capacity. Interfacial failure also prevents the panel material, even with good intrinsic properties, from fully utilizing its capabilities, and the buffering function of the supporting structure fails due to the loss of panel constraint.

[0004] In conclusion, there is an urgent need for systematic technological breakthroughs at multiple levels, including material formulation design, structural geometry optimization, and manufacturing processes, in order to develop new composite hollow board products with excellent comprehensive performance, long service life, and good economic efficiency. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a composite hollow plate, which includes an outer plate and an inner plate, the outer plate having a thickness of 2-10 mm and the inner plate having a thickness of 2-8 mm; a plurality of corrugated support structures are connected between the outer plate and the inner plate; and there is a cavity between adjacent corrugated support structures.

[0006] In a preferred embodiment, the outer panel comprises the following components in parts by weight:

[0007] Matrix resin: 100-160 parts of epoxy resin E-51; hardener: 20-30 parts of 4,4-diaminodiphenylmethane; wear-resistant reinforcing agent: 5-10 parts of nano-silica, 8-15 parts of silicon carbide micro powder; coupling agent: 1-3 parts of silane coupling agent KH-560; reinforcing fiber: 50-100 parts of chopped glass fiber mat.

[0008] The inner plate is composed of the following components in parts by weight:

[0009] Matrix resin: 100 parts vinyl ester resin, 70-90 parts epoxy acrylate; Linear polymer network: 20-30 parts polyurethane prepolymer; Curing system: 3-5 parts benzoyl peroxide, 0.5-1.5 parts dimethylaniline; Toughening agent: 15-25 parts carboxyl-terminated polybutadiene rubber; Synergistic additive: 4-8 parts maleic anhydride-grafted polypropylene; Self-healing system: 8-15 parts epoxy-amine bicore double-walled microcapsules; Nano-reinforcing agent: 3-6 parts organically modified montmorillonite; Reinforcing fiber: 80-120 parts continuous glass fiber mat;

[0010] The corrugated support structure is composed of the following components in parts by weight:

[0011] First network resin: 100 parts of phthalic unsaturated polyester resin; Second network polyol component: 60-80 parts of polyether polyol, 30-40 parts of castor oil-based polyol; Second network isocyanate component: 40-60 parts of 4,4-diphenylmethane diisocyanate; Reinforcing fiber: 60-90 parts of chopped glass fiber, 40-60 parts of glass fiber nonwoven fabric; Crosslinking agent: 2-4 parts of divinylbenzene; Curing system: 3-5 parts of cyclohexanone peroxide, 0.4-1.0 parts of dibutyltin dilaurate; Shape memory reinforcing agent: 5-10 parts of polycaprolactone diol; Foaming agent: 1-2 parts of azodicarbonamide, 3-5 parts of a composite system of sodium bicarbonate and citric acid; Foaming stabilizer: 0.5-1.5 parts of silicone oil; Nucleating agent: 1-3 parts of nano-calcium carbonate, 2-4 parts of talc.

[0012] In a preferred embodiment, the preparation process of the epoxy-amine bicore double-walled microcapsules includes: using triethylene glycol diepoxyglycerol ether as the core repair agent and diethylenetriamine as the outer core curing agent, preparing the microcapsules by interfacial polymerization, with the inner wall being a polyurethane-urea-formaldehyde resin composite wall material and the outer wall being a polyurea wall material.

[0013] The preparation process of the organically modified montmorillonite includes: dispersing sodium montmorillonite in water at 80-90℃, adding octadecyltrimethylammonium chloride, stirring and reacting at 60-70℃ for 2-4 hours, and washing until no Cl is found. - After ionization, drying and grinding were performed to obtain organically modified montmorillonite;

[0014] The polyurethane prepolymer is castor oil type with a molecular weight of 1500-2500, the polyether polyol has a molecular weight of 2000-3000, and the polycaprolactone diol has a molecular weight of 800-1200.

[0015] This invention provides a process for preparing composite hollow plates, comprising the following steps:

[0016] S1: Prepare an interface-reinforced coating. Prepare interface-reinforced coating component A and component B respectively. Component A is used for fiber pretreatment of the outer and inner panels, and component B is used for interface reinforcement of the corrugated support structure surface.

[0017] S2: Prepare a three-cavity partitioned mold, including an outer plate forming cavity, an inner plate forming cavity and a corrugated support structure forming cavity, install an electrode plate system and a multi-point gating system on the mold, and configure a temperature partitioned control system and a pressure monitoring system.

[0018] S3: Perform interface pretreatment. After coating the cut short glass fiber mat and continuous glass fiber mat with the interface reinforcement coating component A, place them in the corresponding outer plate forming cavity and inner plate forming cavity, with the coating surface facing inward.

[0019] S4: Prepare the outer plate material, inner plate material and corrugated support structure material separately. When preparing the inner plate material, first pre-disperse the organic modified montmorillonite in part of the epoxy acrylate resin and then mix it with the main resin. When preparing the corrugated support structure material, prepare component A and component B separately. Adjust the viscosity of each material system and control the viscosity ratio of the three layers of materials within the range of 1:0.8-1.2. After vacuum degassing, transfer each material to the reaction injection machine tank.

[0020] S5: The pulsed electric field assisted reaction injection molding process is adopted. The outer plate material, corrugated support structure material and inner plate material are injected in three stages in sequence. During the second stage injection, the interface reinforcement coating component B is simultaneously coated on the surface of the corrugated support structure. When the initial viscosity of the resin reaches 0.5-1.0 Pa·s, the pulsed electric field is applied to promote interfacial bonding and fiber wetting. The pulsed electric field parameters are electric field strength 0.2-0.8 kV / mm, pulse frequency 50-150 Hz, duty cycle 20-40%, and the injection interval between each stage is controlled within 30-90 seconds.

[0021] S6: Perform simultaneous curing and post-treatment. After the three-stage injection is completed, the temperature zone control allows each layer of material to complete the main curing reaction and form an interface bond within 15-30 minutes. After confirming that the curing degree of each layer reaches more than 85% through online monitoring, the mold is cooled and demolded. Finally, the demolded composite hollow board is post-cured.

[0022] In the preferred embodiment, step S1 includes:

[0023] S11: Prepare component A of the interface-enhancing coating, according to the following mass ratio: 70-80 parts of epoxy resin E-44, 15-25 parts of polyurethane prepolymer, 2-3 parts of silane coupling agent KH-550, and 0.5-1.5 parts of nano-graphene.

[0024] S12: When preparing component A of the interface-reinforced coating, epoxy resin E-44, polyurethane prepolymer, and silane coupling agent KH-550 are stirred at 50-70℃ for 60-90 minutes to ensure that the components are fully mixed and homogeneous. At the same time, nano-graphene is pre-dispersed in anhydrous ethanol and ultrasonically treated for 15-30 minutes. Then, the nano-graphene dispersion is added to the resin mixture and stirred for 30-60 minutes. After standing and degassing for 20-40 minutes, component A of the interface-reinforced coating is obtained.

[0025] S13: Formulate component B of the interface-enhancing coating according to the following mass ratio: 60-70 parts of unsaturated polyester resin, 25-35 parts of epoxy acrylate, 2-3 parts of silane coupling agent KH-560, and 0.3-0.8 parts of functionalized carbon nanotubes.

[0026] S14: When preparing component B of the interface-reinforced coating, unsaturated polyester resin, epoxy acrylate, and silane coupling agent KH-560 are stirred at 50-70℃ for 60-90 minutes to ensure that the components are fully mixed and homogeneous. At the same time, functionalized carbon nanotubes are pre-dispersed in acetone and ultrasonically treated for 15-30 minutes. Then, the carbon nanotube dispersion is added to the resin mixture and stirred for 30-60 minutes. After standing and degassing for 20-40 minutes, component B of the interface-reinforced coating is obtained.

[0027] In the preferred embodiment, step S2 includes:

[0028] S21: Design and process the three-cavity partition mold body, dividing the mold into three independent forming cavities. The outer plate forming cavity and the inner plate forming cavity are flat cavities, and the corrugated support structure forming cavity is designed as a corrugated curved surface. A sealing partition is set between each forming cavity to prevent different materials from penetrating each other. The mold is manufactured using CNC milling or EDM and the geometric accuracy of the curved surface is ensured.

[0029] S22: Gates are provided at the crests and troughs of the corrugated support structure molding cavity, with a gate spacing of 80-120mm and a gate diameter of 3-6mm. Each gate is equipped with a needle valve nozzle controlled by a solenoid valve to open and close. 3-5 gates are evenly arranged in the outer plate molding cavity and the inner plate molding cavity, with a gate diameter of 4-8mm. A venting groove is provided at the highest point of the mold, with a venting groove depth of 0.02-0.05mm.

[0030] S23: Electrode grooves are opened on the upper and lower surfaces of the mold at a distance of 5-10mm from the surface of the forming cavity. The electrode plate is embedded in the electrode groove and sealed with insulating epoxy resin. The electrode leads are led out from the side of the mold and connected to the pulse power supply. The upper surface electrode is connected to the positive terminal and the lower surface electrode is connected to the negative terminal.

[0031] S24: Install heating rods and temperature sensors around each molding cavity, set different target temperatures in different areas of the corrugated support structure molding cavity to achieve temperature gradient control, install pressure sensors in each molding cavity with a range of 0-5MPa, and connect all sensors and control devices to the PLC control system.

[0032] In the preferred embodiment, step S3 includes:

[0033] S31: Cut the fiber reinforcement according to the size of the forming cavity. Cut the chopped glass fiber mat to the size that matches the outer plate forming cavity, and cut the continuous glass fiber mat to the size that matches the inner plate forming cavity. Check the integrity of the fiber mat to ensure that there is no damage or defects.

[0034] S32: Apply the interface reinforcement coating component A to the fiber reinforcement using an ultrasonic atomization spraying device. Load the prepared interface reinforcement coating component A into the material tank of the spraying device, set the ultrasonic frequency to 1.7-2.4MHz to make the coating atomization particle size reach 5-15μm, adjust the vertical distance between the spray gun and the surface of the fiber felt to 15-25cm, and apply the coating evenly using a reciprocating spraying path. Control the coating thickness to 50-150μm, and use a thickness gauge to check the uniformity of the coating thickness.

[0035] S33: Place the coated fiber felt in the molding cavity. The chopped glass fiber felt coated with component A of the interface reinforcement coating is laid flat in the outer plate molding cavity with the coated side facing inward. Ensure that the fiber felt adheres well to the cavity wall without bubbles or wrinkles. Similarly, the coated continuous glass fiber felt is laid in the inner plate molding cavity. Close the mold and apply pre-tightening force to seal the mold.

[0036] In the preferred embodiment, step S4 includes:

[0037] S41: Prepare the outer panel material. Add epoxy resin E-51 to a planetary mixer and stir at 60-80℃ to ensure the resin is fully mixed. Pre-wet nano-silica and silicon carbide micro powder in silane coupling agent KH-560 for 30-60 minutes and then slowly add them to the resin. Stir at high speed at 70-90℃ for 30-50 minutes to ensure the filler is fully dispersed. Add hardener 4,4-diaminodiphenylmethane and stir rapidly for 5-10 minutes. Then degas under vacuum for 15-30 minutes and adjust the viscosity to 0.3-0.8 Pa·s to obtain the outer panel reaction mixture.

[0038] S42: To prepare the inner plate material, first, ultrasonically disperse the organically modified montmorillonite in epoxy acrylate for 20-40 minutes. After adding the dispersant, mix under high shear for 10-20 minutes. Then, add the vinyl ester resin, polyurethane prepolymer, carboxyl-terminated polybutadiene rubber toughening agent, and maleic anhydride-grafted polypropylene synergist in sequence. Stir and mix for 10-15 minutes after each addition. Slowly add the epoxy-amine bicore double-walled microcapsules and stir at low speed to ensure uniform dispersion, avoiding damage to the microcapsules by high-speed stirring. Add the benzoyl peroxide initiator and dimethylaniline accelerator and stir rapidly for 3-5 minutes. Degas under vacuum for 15-30 minutes and adjust the viscosity to 0.4-0.9 Pa·s to obtain the inner plate reaction mixture.

[0039] S43: To prepare component A of the corrugated support structure material, stir the phthalic unsaturated polyester resin and divinylbenzene crosslinking agent at 50-70℃ for 30-50 minutes to ensure thorough mixing. Then, add the azodicarbonamide foaming agent, sodium bicarbonate and citric acid composite foaming agent, nano-calcium carbonate and talc nucleating agent, and silicone oil foaming stabilizer in sequence. Stir and mix for 10-20 minutes after each addition. Add the chopped glass fibers in batches and stir at low speed to ensure uniform fiber dispersion. Add the cyclohexanone peroxide initiator and stir rapidly for 3-5 minutes. Adjust the viscosity to 0.1-0.3 Pa·s to obtain component A of the corrugated support structure material.

[0040] S44: To prepare component B of the corrugated support structure material, mix polyether polyol and castor oil-based polyol at a mass ratio of 2:1, stir at 40-60℃ for 30-50 minutes to ensure thorough mixing of the two polyols, add polycaprolactone diol shape memory enhancer and stir at 50-70℃ for 20-40 minutes to ensure full integration, add dibutyltin dilaurate catalyst and stir for 5-10 minutes, weigh the corresponding amount of 4,4-diphenylmethane diisocyanate, slowly add it to the polyol mixture and stir rapidly for 10-15 minutes to ensure thorough mixing, adjust the viscosity to 0.1-0.3 Pa·s to obtain component B of the corrugated support structure material;

[0041] S45: Transfer the prepared materials to the reaction injection machine, transfer the outer plate reaction mixture to the outer plate material tank, transfer the inner plate reaction mixture to the inner plate material tank, and transfer the corrugated support structure material components A and B to their respective tanks. Set the temperature of each tank to 50-60℃ for the outer plate tank, 45-55℃ for the inner plate tank, and 40-50℃ for the corrugated support structure material tank. Turn on the circulation system to prevent material sedimentation and pre-gelling. After checking that the liquid level, temperature, and circulation pressure of each tank are normal, it is ready for use.

[0042] In the preferred embodiment, step S5 includes:

[0043] S51: Set the pulse electric field parameters and perform the first stage injection. In the PLC control system, set the pulse electric field parameters as follows: electric field strength 0.2-0.8kV / mm, pulse frequency 50-150Hz, duty cycle 20-40%. Start the outer plate material gate, set the injection pressure to 0.8-1.2MPa, and the mold filling speed to 300-500g / s. When the viscosity of the outer plate reaction mixture reaches 0.5-1.0Pa·s, the pulse power supply is started to apply the pulse electric field. Under the action of injection pressure and electric field, the outer plate reaction mixture enters the outer plate molding cavity and gradually impregnates the chopped glass fiber mat. When the pressure in the outer plate molding cavity reaches the set value and stabilizes, close the outer plate material gate to complete the first stage injection.

[0044] S52: Perform the second stage injection. Within 30-90 seconds after the first stage injection is completed, immediately start the injection of corrugated support structure material. Pressurize component A and component B to 10-20MPa respectively through a metering pump and deliver them to the high-pressure impact mixing head at a mass ratio of 1:0.8-1.2. The mixing head has a counter-impact structure inside, so that component A and component B are mixed at high speed and flow out immediately. Set the injection pressure to 0.5-0.9MPa. Use gate opening sequence control to open the gates from the center to both sides one by one to ensure uniform mold filling.

[0045] S53: During the second stage of injection, the interface reinforcement coating component B is applied simultaneously. The interface reinforcement coating component B is sprayed onto the surface of the corrugated support structure while the corrugated support structure material is being injected using a preset coating system. The coating thickness is controlled at 30-100μm. A pulsed electric field is continuously applied to promote interfacial bonding. The second stage of injection is completed when the pressure in the curved surface forming cavity is stable.

[0046] S54: Perform the third stage injection. Immediately after the second stage injection is completed, start the injection of the inner plate material. Start the inner plate material gate, set the injection pressure to 0.7-1.1MPa, and the mold filling speed to 350-550g / s. The inner plate reaction mixture enters the inner plate molding cavity under the action of injection pressure and electric field and impregnates the continuous glass fiber mat. Control the contact interface temperature between the inner plate material and the corrugated support structure material at 45-55℃ to ensure good interface bonding. When the pressure in the inner plate molding cavity is stable, close the inner plate material gate, stop the pulse electric field, and complete the third stage injection.

[0047] S55: Monitors the filling status and adjusts the curing temperature. The PLC control system collects the pressure and temperature data of each molding cavity in real time, analyzes the pressure curve to determine the filling completion status of each cavity, and records the filling completion time of each layer. After the three-stage injection is completed, the PLC control system automatically switches to the curing temperature control mode, adjusts the temperature of the outer and inner plate molding cavities to 50-60℃ to promote resin curing, and maintains the temperature gradient distribution of the corrugated support structure molding cavity to achieve graded foaming.

[0048] In the preferred embodiment, step S6 includes:

[0049] S61: Synchronous curing is performed to maintain stable temperature in each molding cavity. The PLC control system monitors the temperature and pressure changes in each molding cavity in real time. The epoxy resin and hardener in the outer panel material undergo a curing reaction. The vinyl ester resin in the inner panel material undergoes free radical polymerization under the action of the initiator, while the polyurethane prepolymer forms a linear network to form a semi-interpenetrating network structure. The unsaturated polyester resin and polyurethane elastomer in the corrugated support structure material crosslink to form a synchronous interpenetrating network structure. Temperature zoning control ensures that each layer completes the main curing reaction within 15-30 minutes. The curing degree of each layer is confirmed to reach more than 85% by DSC or infrared monitoring.

[0050] S62: Perform mold cooling and demolding. After curing, the PLC control system shuts down the heating system and starts the cooling system. Cooling water is circulated through the cooling water pipeline, and the cooling rate is controlled at 2-5℃ / min to avoid internal stress. When the mold temperature drops to 40-45℃ and remains stable for more than 10 minutes, the PLC control system sends a demolding signal and starts the hydraulic system to open the mold. The mold opening speed is 10-30mm / min. Use demolding tools to gently remove the composite hollow board from the mold.

[0051] S63: Perform post-curing treatment. Place the demolded composite hollow board in a special post-curing oven. Set the oven temperature to 80-120℃ and the heating rate to 2-5℃ / min. After the oven temperature reaches the set temperature, keep it at that temperature for 2-4 hours to perform post-curing treatment to eliminate internal stress and improve the degree of curing. After the post-curing treatment is completed, turn off the oven heating system and let it cool naturally to below 60℃. Open the oven door to allow the product to continue cooling to room temperature inside the oven. The cooling rate should not exceed 3℃ / min.

[0052] The beneficial effects achieved by this invention are as follows:

[0053] First, the composite hollow board designed in this invention incorporates nano-silica and silicon carbide micropowder as wear-resistant reinforcing agents in the outer panel material, and forms a stable dispersion system with a silane coupling agent. This allows the outer panel to maintain high rigidity and support strength while possessing excellent wear resistance. The three-dimensional cross-linked network formed by the epoxy resin and hardener during the curing process provides the outer panel with basic load-bearing capacity, while the addition of the wear-resistant reinforcing agents significantly improves the wear resistance of the outer panel surface through crack deflection and pinning mechanisms. This enables the composite hollow board to withstand repeated contact friction without surface damage in steel coil packaging applications. Chopped glass fiber mat is uniformly dispersed in the resin matrix to form a reinforcing skeleton, ensuring that the outer panel does not undergo brittle fracture under bending loads, while maintaining appropriate elastic deformation capacity to adapt to the deformation requirements during steel coil packaging.

[0054] Secondly, the composite hollow board designed in this invention uses vinyl ester resin and epoxy acrylate as the main matrix resins in the inner board material, and introduces polyurethane prepolymer to form a semi-interpenetrating network structure. This unique network structure design allows the inner board to have sufficient supporting stiffness while producing moderate elastic deformation when bearing the weight of the steel coil. Carboxyl-terminated polybutadiene rubber is dispersed in the resin matrix as a toughening agent to form an island structure. Under impact load, the rubber phase can absorb a large amount of impact energy through crazing and voiding mechanisms, significantly improving the toughness and impact resistance of the inner board. Maleic anhydride-grafted polypropylene, as a synergistic additive, improves the interfacial compatibility between the rubber phase and the resin phase, ensuring that the toughening agent can play its full role. More importantly, this invention introduces an epoxy-amine bicore double-walled microcapsule self-healing system into the inner panel material. When microcracks are generated in the inner panel during use, the microcapsules rupture under the stress at the crack, releasing the repair agent and curing agent. The two undergo an in-situ polymerization reaction at the crack to fill the crack and form a chemical bond with the matrix material, realizing the automatic repair function of the crack, improving the damage tolerance of the inner panel and significantly extending its service life.

[0055] Third, this invention employs a synchronous interpenetrating network design in the corrugated support structure material. A first network is formed by the cross-linking of phthalic unsaturated polyester resin and divinylbenzene in component A, while a second network is formed by the reaction of polyol and diisocyanate in component B to form a polyurethane elastomer. These two networks form synchronously and interpenetrate each other during the reaction process. This network structure allows the corrugated support structure to undergo significant elastic deformation and effectively absorb impact energy under pressure. The introduction of polycaprolactone diol as a shape memory enhancer enables the corrugated support structure to possess shape memory properties. Its crystalline phase acts as the fixed phase to maintain a permanent shape, while the amorphous phase acts as a reversible phase to achieve shape transformation. When the composite hollow board deforms under external extrusion during steel coil packaging and transportation, it can quickly return to its original shape, ensuring that the packaging material can be reused repeatedly without experiencing a decrease in cushioning performance due to cumulative deformation. The microporous structure generated during the curing process of the foaming agent system further enhances the cushioning and energy absorption capacity of the corrugated support structure while effectively reducing the overall weight.

[0056] Fourth, this invention employs a corrugated support structure design to replace the traditional straight structure. When subjected to compressive loads, the corrugated curve first bends and deforms at the locations with higher curvature. As the load increases, the deformation gradually extends to the entire corrugated curve. This progressive deformation characteristic results in a more uniform stress distribution, avoiding the stress concentration problem at the turning points of the straight structure. The corrugated design can maintain a relatively stable stress level over a large deformation range, forming a distinct plateau region, thereby achieving efficient energy absorption and providing excellent protection against various impact loads during the transportation of steel coil packaging. The corrugated surface structure also allows the outer plate, inner plate, and corrugated support structure to deform collaboratively under stress, significantly improving the overall structure's buffering performance and fatigue stability.

[0057] Fifth, this invention employs pulsed electric field-assisted reaction injection molding technology in its manufacturing process, coupled with a specially designed interface-enhancing coating. By pre-coating the fiber reinforcement surface with an interface-enhancing coating containing silane coupling agents and nano-reinforcing materials, favorable conditions are created for subsequent resin wetting and interfacial bonding. The application of the pulsed electric field causes the resin molecular dipoles to orient along the electric field direction, thereby reducing the apparent viscosity of the system. Simultaneously, the electric field force drives charged ions and polar molecules to migrate to the fiber surface, accelerating the interfacial chemical reaction. This improves the resin's wetting performance on the fiber and allows it to penetrate deeper into the fiber bundle, forming more chemical bonding points and a denser transition layer structure at the fiber-resin interface. This significantly improves the interfacial bonding strength and interlaminar shear strength between the outer plate, inner plate, and corrugated support structure, ensuring that the multilayer composite structure can synergistically bear loads without delamination failure. This provides a reliable foundation for the overall structure to exert its toughening, self-healing, and shape memory functional characteristics. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the structure of the composite hollow plate of the present invention;

[0059] Figure 2 This is a flowchart of the preparation method of the composite hollow plate of the present invention;

[0060] Figure 3 This is a comparison chart of key performance indicators of the embodiments and comparative examples of the present invention.

[0061] Figure 4 This is a comparison chart of the shape recovery rate indicators between Example 1 and Comparative Example 3;

[0062] Figure 5 This is a schematic diagram of the stress-strain curve, crack width-time curve, and wetting depth-time curve of the embodiments and comparative examples of the present invention.

[0063] Numbering on the map:

[0064] 1. Outer panel; 2. Inner panel; 3. Corrugated support structure. Detailed Implementation

[0065] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0066] Example 1, referring to Figures 1-2 This embodiment describes the preparation of a composite hollow board for packaging steel coils. The composite hollow board includes an outer board 1 and an inner board 2. The outer board 1 has a thickness of 6 mm, and the inner board 2 has a thickness of 5 mm. The outer board and the inner board are connected by several corrugated support structures 3, and a cavity structure is formed between adjacent corrugated support structures 3. The corrugated support structures have an S-shaped curved surface.

[0067] In the embodiments of this invention, all parts are by weight, used to characterize the mass ratio between the components. This ratio is fixed, but the total mass required for specific implementation can be scaled up or down by those skilled in the art, based on the needs of actual production scale, while maintaining the stated ratio.

[0068] The outer panel material is prepared according to the following weight ratios: 130 parts of epoxy resin E-51 as the matrix resin, 25 parts of 4,4-diaminodiphenylmethane as the hardener, 7.5 parts of nano-silica and 11.5 parts of silicon carbide micropowder as wear-resistant reinforcing agents, 2 parts of silane coupling agent KH-560, and 75 parts of chopped glass fiber mat as reinforcing fibers. During the curing process, the epoxy resin E-51 and the hardener 4,4-diaminodiphenylmethane form a three-dimensional cross-linked network in the outer panel material. This network structure imparts high rigidity and support strength to the outer panel. The nano-silica and silicon carbide micropowder, as wear-resistant reinforcing agents, significantly improve the wear resistance of the outer panel surface, which is of great significance for the repeated contact and friction conditions in steel coil packaging applications. The chopped glass fiber mat is uniformly dispersed in the resin matrix to form a reinforcing skeleton, ensuring support strength while giving the outer panel a certain degree of elastic deformation capability.

[0069] When preparing the inner panel material, it is formulated according to the following weight ratios: 100 parts vinyl ester resin and 80 parts epoxy acrylate in the matrix resin; 25 parts polyurethane prepolymer in the linear polymer network; 4 parts benzoyl peroxide and 1 part dimethylaniline in the curing system; 20 parts carboxyl-terminated polybutadiene rubber as toughening agent; 6 parts maleic anhydride-grafted polypropylene as synergistic agent; 11.5 parts epoxy-amine bicore double-walled microcapsules as self-healing system; 4.5 parts organically modified montmorillonite as nano-reinforcing agent; and 100 parts continuous glass fiber mat as reinforcing fiber. In the inner panel material system, vinyl ester resin and epoxy acrylate resin serve as the main matrix resins, providing basic mechanical properties. During the curing process, the polyurethane prepolymer forms a linear polymer network and a semi-interpenetrating network structure with the main resin. This semi-interpenetrating network structure enables the inner panel to have sufficient supporting stiffness while producing moderate elastic deformation when bearing the weight of the steel coil. Carboxyl-terminated polybutadiene rubber, as a toughening agent, significantly improves the toughness and impact resistance of the inner panel. Maleic anhydride-grafted polypropylene, as a synergistic additive, can improve the interfacial compatibility between the rubber phase and the resin phase. Epoxy-amine bicore double-walled microcapsules, as a self-healing system, are dispersed in the resin matrix. When microcracks occur in the inner panel during use, the microcapsules rupture and release the core triethylene glycol diepoxyglycerol ether repair agent and the outer core diethylenetriamine curing agent. The two react at the crack to achieve self-healing of the crack. The continuous glass fiber mat provides good overall strength for the inner panel.

[0070] When preparing the corrugated support structure material, components A and B are formulated according to the following weight ratios. Component A includes 100 parts of phthalic unsaturated polyester resin as the first network resin, 75 parts of chopped glass fiber and 50 parts of glass fiber nonwoven fabric as reinforcing fibers, 3 parts of divinylbenzene as a crosslinking agent, 4 parts of cyclohexanone peroxide and 0.7 parts of dibutyltin dilaurate as the curing system, 7.5 parts of polycaprolactone diol as a shape memory reinforcing agent, 1.5 parts of azodicarbonamide and 4 parts of a composite system of sodium bicarbonate and citric acid as a foaming agent, 1 part of silicone oil as a foaming stabilizer, and 2 parts of nano-calcium carbonate and 3 parts of talc as nucleating agents. Component B includes 70 parts of polyether polyol and 35 parts of castor oil-based polyol as the second network polyol component, and 50 parts of 4,4-diphenylmethane diisocyanate as the second network isocyanate component. The corrugated support structure material adopts a synchronous interpenetrating network design. In component A, the phthalic unsaturated polyester resin crosslinks with divinylbenzene to form the first network, while in component B, the polyol reacts with diisocyanate to form a polyurethane elastomer, constituting the second network. The two networks are formed synchronously and interpenetrate each other during the reaction process. This synchronous interpenetrating network structure enables the corrugated support structure to undergo large elastic deformation under compression. When the composite hollow board is subjected to external extrusion pressure during steel coil packaging and transportation, the S-shaped corrugated support structure first deforms to absorb some energy, and the outer and inner panels also undergo slight elastic deformation. The deformation process effectively buffers the extrusion pressure. Polycaprolactone diol, as a shape memory reinforcing agent, endows the corrugated support structure with shape memory characteristics. When the extrusion pressure disappears, the outer and inner panels and the corrugated support structure can return to their original shape by relying on the shape memory effect and elastic recovery force. The foaming agent system generates gas during the curing process to form a microporous structure. The microporous structure further enhances the buffering and energy absorption capacity of the corrugated support structure, while reducing the overall weight.

[0071] In the preparation of epoxy-amine bicore double-walled microcapsules, triethylene glycol diepoxyglycerol ether was first used as the core repair agent. Its epoxy groups can undergo ring-opening polymerization under the action of the curing agent to achieve the repair function. Diethylenetriamine was used as the outer core curing agent and prepared by interfacial polymerization. The core repair agent was mixed with polyurethane prepolymer and urea-formaldehyde resin prepolymer in the aqueous phase. Through interfacial polymerization, a polyurethane-urea-formaldehyde resin composite inner wall was formed on the surface of the oil droplet. The thickness of the inner wall was about 2-3 μm. Then, the outer core curing agent was further coated on the outside of the inner wall. Through interfacial polymerization, a polyurea outer wall was formed. The thickness of the outer wall was about 1-2 μm. The bicore double-walled structure ensures that the repair agent and the curing agent are isolated from each other when the microcapsule is intact. They can only come into contact and react when the microcapsule is broken due to microcracks.

[0072] In the preparation of organically modified montmorillonite, sodium-based montmorillonite was fully dispersed in water at 85°C. The montmorillonite lamellar structure swelled and peeled in water. Then, octadecyltrimethylammonium chloride was added as an organic modifier. The long-chain alkyl groups in octadecyltrimethylammonium chloride could intercalate into the interlayer spaces of the montmorillonite lamellars. The reaction was stirred at 65°C for 3 hours to allow the organic modifier to fully react with the montmorillonite. During the reaction, the quaternary ammonium cations in octadecyltrimethylammonium chloride exchanged ions with the sodium ions between the montmorillonite lamellars. The long organic chains intercalated into the interlayer spaces, increasing the interlayer spacing. The mixture was washed until no Cl was found. - After ionization, the material is dried and ground to obtain organically modified montmorillonite. The organically modified montmorillonite exhibits significantly improved dispersibility and compatibility in the resin matrix. The polyurethane prepolymer selected is castor oil type with a molecular weight of 2000, the polyether polyol with a molecular weight of 2500, and the polycaprolactone diol with a molecular weight of 1000.

[0073] In the preparation of the interface-reinforced coating in step S1, component A of the interface-reinforced coating was first prepared according to the following mass ratio: 75 parts epoxy resin E-44, 20 parts polyurethane prepolymer, 2.5 parts silane coupling agent KH-550, and 1 part graphene nanoparticles. In the specific operation of preparing component A, epoxy resin E-44, polyurethane prepolymer, and silane coupling agent KH-550 were placed in a reaction vessel and stirred at 60°C for 75 minutes to ensure thorough and uniform mixing of the components. Thorough mixing of the resin components lays the foundation for the subsequent dispersion of the nanomaterials. Simultaneously, the graphene nanoparticles were pre-dispersed in anhydrous ethanol and ultrasonically treated for 20 minutes using an ultrasonic processor. Ultrasonic treatment effectively exfoliates the aggregated graphene sheets. Then, the graphene nanoparticle dispersion was slowly added to the resin mixture and stirred for another 45 minutes. After standing and degassing for 30 minutes, component A of the interface-reinforced coating was obtained. In component A of the interface-reinforcing coating, epoxy resin E-44 forms a gradient structure with the polyurethane prepolymer. The siloxane groups in the silane coupling agent KH-550 can chemically bond with the hydroxyl groups on the glass fiber surface, and the amino groups can react with the epoxy resin, thereby forming a strong chemical bond between the fiber and the resin matrix. The addition of nano-graphene significantly improves the mechanical and electrical properties of the interface region, and the two-dimensional sheet structure of nano-graphene can effectively prevent crack propagation. Then, component B of the interface-reinforcing coating is prepared according to the following mass ratio: 65 parts unsaturated polyester resin, 30 parts epoxy acrylate, 2.5 parts silane coupling agent KH-560, and 0.5 parts functionalized carbon nanotubes. In preparing component B of the interface-reinforced coating, unsaturated polyester resin, epoxy acrylate, and silane coupling agent KH-560 were stirred at 60°C for 75 minutes to ensure thorough and uniform mixing. Simultaneously, functionalized carbon nanotubes were pre-dispersed in acetone and ultrasonically treated for 20 minutes. Then, the carbon nanotube dispersion was added to the resin mixture and stirred for another 45 minutes. After standing and degassing for 30 minutes, component B of the interface-reinforced coating was obtained. The functionalized carbon nanotubes formed a reinforcing layer on the surface of the corrugated support structure. The high aspect ratio and excellent mechanical properties of the carbon nanotubes significantly improved the interfacial strength.

[0074] When preparing the three-cavity partitioned mold in step S2, the main body of the three-cavity partitioned mold is first designed and processed, dividing the mold into three independent forming cavities. The outer plate forming cavity is a flat cavity with dimensions of 2000mm×1000mm×6mm, and the inner plate forming cavity is also a flat cavity with dimensions of 2000mm×1000mm×5mm. The corrugated support structure forming cavity is designed with an S-shaped corrugated surface with a corrugation height of 40mm and a corrugation spacing of 80mm. The radius of curvature of the S-shaped surface varies continuously within the range of 20-60mm. Sealed partitions are set between each forming cavity to prevent different materials from penetrating each other. The mold is processed using a CNC milling machine, and the geometric accuracy of the S-shaped surface is ensured to reach ±0.1mm. Then, gates are set at the crests and troughs of the corrugated support structure molding cavity, with a gate spacing of 100mm and a gate diameter of 4.5mm. Each gate is equipped with a needle valve nozzle controlled by a solenoid valve to open and close. The solenoid valve response time is less than 50ms to ensure precise control. Four gates with a gate diameter of 6mm are evenly arranged in the outer plate molding cavity, and four gates with a gate diameter of 6mm are evenly arranged in the inner plate molding cavity. A venting groove is set at the highest point of the mold, with a depth of 0.03mm and a width of 5mm. Next, electrode grooves are made on the upper and lower surfaces of the mold at a distance of 7.5mm from the surface of the molding cavity. The electrode grooves are 15mm deep and 20mm wide. Copper electrode plates are embedded in the electrode grooves and sealed with insulating epoxy resin. The electrode plate thickness is 10mm. Electrode leads are led out from the side of the mold and connected to a pulse power supply. The upper surface electrode is connected to the positive terminal, and the lower surface electrode is connected to the negative terminal. The electrode leads are insulated with high-temperature resistant silicone rubber. Then, heating rods and temperature sensors are installed around each molding cavity. Six heating rods with a power of 1000W are evenly arranged around the outer plate molding cavity, and six heating rods with a power of 1000W are evenly arranged around the inner plate molding cavity. The corrugated support structure molding cavity is divided into three areas with different target temperatures to achieve temperature gradient control: the target temperature of the central area is 55℃, and the target temperature of the edge area is 45℃. Pressure sensors with a range of 0-5MPa and an accuracy class of 0.5 are installed in each molding cavity. All sensors and control devices are connected to the PLC control system, which uses a scanning cycle of 10ms to collect data in real time.

[0075] When performing interface pretreatment in step S3, the fiber reinforcement is first cut according to the size of the forming cavity. The chopped glass fiber mat is cut into 2000mm×1000mm pieces to match the outer plate forming cavity, and the continuous glass fiber mat is cut into 2000mm×1000mm pieces to match the inner plate forming cavity. Special cutting shears are used during cutting to ensure that the edges are neat. The integrity of the fiber mat is checked to ensure that there is no damage or defects. Then, the interface reinforcement coating component A was coated onto the fiber reinforcement using an ultrasonic atomization spraying device. The prepared interface reinforcement coating component A was loaded into the material tank of the spraying device, and the ultrasonic frequency was set to 2MHz to achieve a coating atomization particle size of 10μm. The small atomization particle size ensures that the coating penetrates into the fiber bundle. The vertical distance between the spray gun and the fiber felt surface was adjusted to 20cm, and a reciprocating spraying path was used for uniform coating. The spraying speed was 300mm / s, the reciprocating interval was 50mm, and the coating thickness was controlled at 100μm. The coating thickness was measured at 10 random points on the fiber felt surface using a thickness gauge, and the thickness uniformity deviation was less than ±10μm. Next, the coated fiber felt is laid in the molding cavity. The chopped glass fiber felt coated with component A of the interface reinforcement coating is laid flat in the outer plate molding cavity with the coated side facing inward. A rubber roller is used to roll from the center to the edge to ensure that the fiber felt adheres well to the cavity wall without bubbles or wrinkles. Similarly, the coated continuous glass fiber felt is laid in the inner plate molding cavity. The mold is closed and a pre-tightening force of 5kN is applied through the hydraulic system to seal the mold.

[0076] When preparing the materials for each layer in step S4, the outer plate material is prepared first. 130 parts of epoxy resin E-51 are added to a planetary mixer and stirred at 70°C for 30 minutes to ensure the resin is fully fluid. 7.5 parts of nano-silica and 11.5 parts of silicon carbide micro powder are pre-wetted in 2 parts of silane coupling agent KH-560 for 45 minutes. The wetting treatment allows the silane coupling agent molecules to form a coating layer on the filler surface. Then, the mixture is slowly added to the resin and stirred at 80°C at a high speed of 800 rpm for 40 minutes to ensure the filler is fully dispersed in the resin matrix. 25 parts of hardener 4,4-diaminodiphenylmethane are added and stirred rapidly for 8 minutes. Then, the mixture is degassed under a vacuum of -0.09 MPa for 20 minutes to remove air bubbles. The viscosity is measured using a rotational viscometer and adjusted to 0.5 Pa·s to obtain the outer plate reaction mixture. Then, the inner plate material was prepared. First, 4.5 parts of organically modified montmorillonite were ultrasonically dispersed in 30 parts of epoxy acrylate for 30 minutes with an ultrasonic power of 500W. Then, 0.5 parts of sodium dodecylbenzenesulfonate dispersant were added and mixed at 3000 rpm for 15 minutes using a high-shear disperser. Then, 100 parts of vinyl ester resin, the remaining 50 parts of epoxy acrylate, 25 parts of polyurethane prepolymer, 20 parts of carboxyl-terminated polybutadiene rubber toughening agent, and 6 parts of maleic anhydride-grafted polypropylene synergist were added sequentially. Each time a component was added, the mixture was stirred for 12 minutes at a stirring speed of 400 rpm. Then, 11.5 parts of epoxy-amine bicore double-walled microcapsules were slowly added and stirred at a low speed of 200 rpm to disperse them evenly for 20 minutes. The low-speed stirring can avoid high-speed shearing damage to the microcapsule wall material. Then, 4 parts of benzoyl peroxide initiator and 1 part of dimethylaniline accelerator were added and stirred rapidly for 4 minutes. Then, the mixture was degassed under vacuum for 20 minutes and the viscosity was adjusted to 0.65 Pa·s to obtain the inner plate reaction mixture. Next, component A of the corrugated support structure material was prepared. 100 parts of phthalic unsaturated polyester resin and 3 parts of divinylbenzene crosslinking agent were stirred at 60°C for 40 minutes to ensure thorough mixing. The addition of the crosslinking agent can control the crosslinking density. 1.5 parts of azodicarbonamide foaming agent, 4 parts of sodium bicarbonate and citric acid composite foaming agent, 2 parts of nano-calcium carbonate nucleating agent, 3 parts of talc nucleating agent, and 1 part of silicone oil foaming stabilizer were added sequentially. Each component was stirred for 15 minutes after addition. 75 parts of chopped glass fiber were added in 3 batches, with each batch stirred for 10 minutes and then stirred at a low speed of 300 rpm to ensure uniform fiber dispersion. 4 parts of cyclohexanone peroxide initiator were added and stirred rapidly for 4 minutes. The viscosity was adjusted to 0.2 Pa·s to obtain component A of the corrugated support structure material.Then, component B of the corrugated support structure material was prepared. 70 parts of polyether polyol and 35 parts of castor oil-based polyol were mixed at a mass ratio of 2:1 and stirred at 50°C for 40 minutes to ensure that the two polyols were fully mixed and homogeneous. The thorough mixing of the polyols ensures the uniformity of the subsequent reaction with isocyanate. 7.5 parts of polycaprolactone diol shape memory enhancer were added and stirred at 60°C for 30 minutes to ensure full integration. 0.7 parts of dibutyltin dilaurate catalyst were added and stirred for 8 minutes. The corresponding amount of 50 parts of 4,4-diphenylmethane diisocyanate was weighed and slowly added to the polyol mixture while stirring and then rapidly stirred for 12 minutes to ensure thorough mixing. The reaction between isocyanate and polyol is an exothermic reaction, and slow addition can control the reaction rate. The viscosity was adjusted to 0.2 Pa·s to obtain component B of the corrugated support structure material. Finally, the prepared materials are transferred to the reaction injection machine. The outer plate reaction mixture is transferred to the outer plate material tank, and the inner plate reaction mixture is transferred to the inner plate material tank. Components A and B of the corrugated support structure material are transferred to their respective tanks. The temperatures of each tank are set as follows: 55℃ for the outer plate tank, 50℃ for the inner plate tank, and 45℃ for the corrugated support structure material tank. The circulation system is turned on with a circulation flow rate of 200L / h to prevent material sedimentation and pre-gelling. The liquid level in each tank is checked to be above 80%, the temperature deviation is less than ±2℃, and the circulation pressure is stabilized at 0.3MPa before use.

[0077] When performing the S5 step using pulsed electric field-assisted reaction injection molding, the pulsed electric field parameters are first set and the first stage injection is performed. In the PLC control system, the pulsed electric field parameters are set as follows: electric field strength 0.5kV / mm, pulse frequency 100Hz, and duty cycle 30%. The application of the pulsed electric field can promote the wetting and penetration of resin molecules on the fiber surface. The outer plate material gate is started, the injection pressure is set to 1MPa, and the mold filling speed is 400g / s. The outer plate reaction mixture is injected into the outer plate molding cavity simultaneously from four gates. When the viscosity of the outer plate reaction mixture reaches 0.7Pa·s, the increase in viscosity indicates that the resin has begun to undergo a gel reaction. At this time, the pulse power supply is started to apply the pulsed electric field. Under the action of the electric field, the dipole orientation of the resin molecules is conducive to improving fiber wetting. Under the action of injection pressure and electric field, the outer plate reaction mixture enters the outer plate molding cavity and gradually impregnates the chopped glass fiber mat. The mold filling time is about 120 seconds. When the pressure in the outer plate molding cavity reaches the set value of 0.8MPa and remains stable for 30 seconds, the outer plate material gate is closed, completing the first stage injection. Within 60 seconds of the completion of the first stage injection, the second stage injection of corrugated support structure material is immediately initiated. Components A and B are pressurized to 15 MPa using a metering pump and delivered to the high-pressure impact mixing head at a 1:1 mass ratio. The flow rates of both components are 200 g / s and 200 g / s. The mixing head has an internal counter-impact structure, where components A and B collide at high speed (approximately 10 m / s). This impact mixing ensures uniform mixing of the two components in a very short time, allowing them to flow out immediately after mixing. The injection pressure is set to 0.7 MPa, and a gate sequence opening control is used. The gate located at the center of the corrugations is opened first, followed by adjacent gates opening sequentially to both sides every 2 seconds. This sequential opening method ensures uniform mold filling from the center outwards, preventing air entrapment. During the second-stage injection process, the interface-enhancing coating component B is simultaneously applied. The interface-enhancing coating component B is sprayed onto the surface of the corrugated support structure being formed through a spraying device that is synchronized with the corrugated support structure material injection system via a preset coating system. The spraying pressure is 0.3 MPa, and the coating thickness is controlled at 65 μm. A pulsed electric field is continuously applied to promote interfacial bonding. The filling time of the corrugated support structure molding cavity is approximately 180 seconds. The second-stage injection is completed when the pressure in the curved surface molding cavity reaches 0.6 MPa and remains stable for 30 seconds.Within 60 seconds of the completion of the second stage injection, the third stage injection of the inner plate material is initiated. The inner plate material gate is opened, the injection pressure is set to 0.9 MPa, and the filling speed is 450 g / s. The inner plate reaction mixture is simultaneously injected into the inner plate molding cavity through four gates. Under the action of injection pressure and electric field, it enters the inner plate molding cavity and impregnates the continuous glass fiber mat. The impregnation of the continuous fibers requires the resin to fully penetrate along the fiber length. The contact interface temperature between the inner plate material and the corrugated support structure material is controlled at 50℃. This temperature ensures that the corrugated support structure material has a certain strength and allows the inner plate material to be fully wetted at the interface to form a good bond. The filling time of the inner plate molding cavity is approximately 110 seconds. When the pressure in the inner plate molding cavity reaches 0.75 MPa and stabilizes for 30 seconds, the inner plate material gate is closed, the pulse electric field is stopped, and the third stage injection is completed. During the injection process, the PLC control system collects pressure and temperature data of each molding cavity in real time at a frequency of 10Hz. The system automatically plots pressure-time curves and temperature-time curves, and analyzes the pressure curves to determine the completion status of each cavity's filling. When the slope of the pressure curve is less than 0.01MPa / s, the filling is considered complete. The completion times of each layer's filling are recorded as follows: 120 seconds for the first stage, 300 seconds for the second stage, and 410 seconds for the third stage. After the three stages of injection are completed, the PLC control system automatically switches to the curing temperature control mode, adjusting the temperature of the outer plate molding cavity to 55℃ and the inner plate molding cavity to 55℃, maintaining the temperature gradient distribution of the corrugated support structure molding cavity, with the central area at 55℃ and the edge area at 45℃. The temperature gradient causes the foaming agent decomposition rate to be distributed in a gradient, achieving graded foaming. The central area foams first and then cures, while the edge area foams later to form a density gradient structure.

[0078] During the simultaneous curing and post-treatment in step S6, the temperature of each molding cavity was first maintained stable. The temperature and pressure changes within each molding cavity were monitored in real time via a PLC control system at 5-second intervals. In the outer panel material, the epoxy resin E-51 and the hardener 4,4-diaminodiphenylmethane underwent a curing reaction. The reaction equation was that the epoxy group reacted with the amino group to generate hydroxylamine and secondary amine. The secondary amine further reacted with the epoxy group to form tertiary amine. The curing process was exothermic. Temperature monitoring showed that the temperature of the outer panel molding cavity rose by approximately 15°C during curing and then gradually decreased. In the inner panel material, the vinyl ester resin underwent free radical polymerization under the action of benzoyl peroxide initiator and dimethylaniline accelerator. The initiator decomposed to generate free radicals that initiated the polymerization of unsaturated double bonds. Simultaneously, the polyurethane prepolymer... The isocyanate groups in the elastomer react with the hydroxyl groups in the resin to form linear polyurethane segments. These linear segments form a semi-interpenetrating network structure with the cross-linked vinyl ester resin network. The semi-interpenetrating network structure has both rigidity and flexibility. The unsaturated polyester resin in the corrugated support structure material cross-links and cures under the action of an initiator to form the first network. The polyurethane elastomer forms the second network through the reaction of polyol and isocyanate. The two networks are formed simultaneously and interpenetrate each other to form a synchronous interpenetrating network structure. Temperature zone control allows each layer of material to complete the main curing reaction within 20 minutes. The degree of curing is monitored by differential scanning calorimetry (DSC). Sampling tests show that the curing degree of the outer panel is 89%, the curing degree of the inner panel is 87%, and the curing degree of the corrugated support structure is 88%, all of which meet the requirement of more than 85%. After curing, the PLC control system shuts down the heating system and starts the cooling system. Cooling water circulates through the internal cooling water pipes of the mold. The inlet temperature of the cooling water is 20℃, the flow rate is 10L / min, and the cooling rate is controlled at 3℃ / min. Slow cooling helps to avoid the generation of internal stress. When the mold temperature drops to 42℃ and stabilizes for 15 minutes, the PLC control system sends a demolding signal, activating the hydraulic system to open the mold. The opening force is set to 50kN, and the opening speed is 20mm / min. The mold stops when the opening gap reaches 50mm. A special demolding tool with a suction cup frame structure is used to gently remove the composite hollow board from the mold. Care is taken to protect the corrugated support structure from damage during demolding. After demolding, the composite hollow board is visually inspected and shows a smooth surface without bubbles. The corrugated support structure is intact, and the outer and inner panels are firmly connected by the S-shaped corrugated support structure.The demolded composite hollow board is placed in a dedicated post-curing oven. The post-curing oven is a hot air circulation type with a temperature uniformity of ±3℃. The post-curing temperature is selected as 100℃ according to the resin system, with a heating rate of 3℃ / min. It takes about 25 minutes to heat from room temperature to 100℃. After the oven temperature reaches the set temperature of 100℃, it is kept at this temperature for 3 hours for post-curing. During the post-curing process, the remaining unreacted groups continue to react, which further improves the degree of curing. At the same time, the internal stress is relaxed. After the heat preservation is completed, the oven heating system is turned off, and the oven door is kept closed to allow the product to cool naturally to 55℃ in the oven, which takes about 4 hours. Then the oven door is opened to allow the product to continue cooling to room temperature of 25℃, with the cooling rate controlled at 2℃ / min. The entire post-curing and cooling process takes about 8 hours.

[0079] Performance tests were conducted on the post-cured composite hollow boards. Bending strength was tested using a universal testing machine according to GB / T1449-2005 "Test Method for Bending Properties of Fiber Reinforced Plastics". The sample size was 80mm × 10mm × board thickness, with a span of 64mm and a loading speed of 2mm / min. The measured bending strength of the outer board was 425MPa, and that of the inner board was 385MPa. Impact strength was tested using a simply supported beam impact testing machine according to GB / T 1043-2008 "Determination of Impact Properties of Simply Supported Beams in Plastics". The sample size was 80mm × 10mm × board thickness, with a notch depth of 2mm. The measured impact strength of the outer board was 42kJ / m². 2 The inner panel impact strength is 58 kJ / m. 2 The compressive resilience of the composite hollow board was tested. The sample was placed on a pressure testing machine, and a pressure of 1 MPa was applied for 10 seconds. The compressive deformation was measured to be 2.3 mm. After unloading, the residual deformation was measured after 60 seconds, and the resilience was 0.15 mm. The resilience rate was calculated to be 93.5%. The formula for calculating the resilience rate η is η = (δ1 - δ2) / δ1 × 100%; where η is the resilience rate (%), δ1 is the maximum compressive deformation (mm), and δ2 is the residual deformation (mm). The high resilience rate indicates that the composite hollow board can effectively recover its original shape after being subjected to compressive loads generated by the weight of the steel coil, which is very important for repeatedly used packaging materials. Shape memory performance tests were conducted on the corrugated support structure. The corrugated support structure was heated to 60℃ to soften it, and an external force was applied to deform it into a temporary shape. The deformed state was maintained and cooled to room temperature to fix the temporary shape. Then, it was reheated to 60℃. It was observed that the corrugated support structure completely recovered to the original S-shaped shape within 5 minutes, with a shape recovery rate of 98%. The realization of the shape memory property is mainly attributed to the polycaprolactone diol shape memory enhancer. The crystalline phase of polycaprolactone diol acts as the fixed phase to maintain the permanent shape, while the amorphous phase acts as the reversible phase to realize the shape transformation.

[0080] Example 2 differs from Example 1 in the choice of material formulation and process parameters. The outer panel material contains 100 parts epoxy resin E-51, 20 parts hardener 4,4-diaminodiphenylmethane, 5 parts nano-silica, 8 parts silicon carbide micropowder, 1 part silane coupling agent KH-560, and 50 parts chopped glass fiber mat. The inner panel material contains 100 parts vinyl ester resin, 70 parts epoxy acrylate, 20 parts polyurethane prepolymer, 3 parts benzoyl peroxide, 0.5 parts dimethylaniline, 15 parts carboxyl-terminated polybutadiene rubber, 4 parts maleic anhydride-grafted polypropylene, 8 parts epoxy-amine bicore double-walled microcapsules, 3 parts organically modified montmorillonite, and 80 parts continuous glass fiber mat. The corrugated support structure material, component A, contains 100 parts of phthalic unsaturated polyester resin, 60 parts of chopped glass fiber, 40 parts of glass fiber nonwoven fabric, 2 parts of divinylbenzene, 3 parts of cyclohexanone peroxide, 0.4 parts of dibutyltin dilaurate, 5 parts of polycaprolactone diol, 1 part of azodicarbonamide, 3 parts of a sodium bicarbonate and citric acid composite system, 0.5 parts of silicone oil, 1 part of nano-calcium carbonate, and 2 parts of talc. The corrugated support structure material, component B, contains 60 parts of polyether polyol, 30 parts of castor oil-based polyol, and 40 parts of 4,4-diphenylmethane diisocyanate. The interface reinforcement coating, component A, contains 70 parts of epoxy resin E-44, 15 parts of polyurethane prepolymer, 2 parts of silane coupling agent KH-550, and 0.5 parts of nano-graphene. The interface-reinforced coating component B contains 60 parts unsaturated polyester resin, 25 parts epoxy acrylate, 2 parts silane coupling agent KH-560, and 0.3 parts functionalized carbon nanotubes. The polyurethane prepolymer has a molecular weight of 1500, the polyether polyol has a molecular weight of 2000, and the polycaprolactone diol has a molecular weight of 800.

[0081] In the pulsed electric field parameter settings, the electric field strength was selected as 0.2 kV / mm, the pulse frequency as 50 Hz, and the duty cycle as 20%. Lower electric field strength and frequency are suitable for resin systems with lower viscosity. The injection pressure for the outer panel material was 0.8 MPa, and the filling speed was 300 g / s. The injection pressure for the inner panel material was 0.7 MPa, and the filling speed was 350 g / s. The injection pressure for the corrugated support structure material was 0.5 MPa. The curing temperatures for each molding cavity were: outer panel 50℃, inner panel 50℃, corrugated support structure center area 50℃, and edge area 40℃. The post-curing temperature was selected as 80℃, with a holding time of 2 hours.

[0082] The composite hollow board prepared in this embodiment was subjected to performance testing. The measured bending strength of the outer board was 365 MPa, the bending strength of the inner board was 325 MPa, and the impact strength of the outer board was 35 kJ / m. 2 The inner panel impact strength is 48 kJ / m. 2The overall compression recovery rate is 90.2%, and the shape recovery rate of the corrugated support structure is 95%. This embodiment uses a lower filler content and fiber content, which makes the material more flexible and elastic. Although the strength is slightly lower than that of Embodiment 1, the recovery performance is still excellent, making it suitable for steel coil packaging scenarios with higher flexibility requirements.

[0083] Example 3 differs from Example 1 in that it uses the upper limit of the formulation range. The outer panel material contains 160 parts epoxy resin E-51, 30 parts hardener 4,4-diaminodiphenylmethane, 10 parts nano-silica, 15 parts silicon carbide micropowder, 3 parts silane coupling agent KH-560, and 100 parts chopped glass fiber mat. The inner panel material contains 100 parts vinyl ester resin, 90 parts epoxy acrylate, 30 parts polyurethane prepolymer, 5 parts benzoyl peroxide, 1.5 parts dimethylaniline, 25 parts carboxyl-terminated polybutadiene rubber, 8 parts maleic anhydride-grafted polypropylene, 15 parts epoxy-amine bicore double-walled microcapsules, 6 parts organically modified montmorillonite, and 120 parts continuous glass fiber mat. The corrugated support structure material, component A, contains 100 parts of phthalic unsaturated polyester resin, 90 parts of chopped glass fiber, 60 parts of glass fiber nonwoven fabric, 4 parts of divinylbenzene, 5 parts of cyclohexanone peroxide, 1 part of dibutyltin dilaurate, 10 parts of polycaprolactone diol, 2 parts of azodicarbonamide, 5 parts of a sodium bicarbonate and citric acid composite system, 1.5 parts of silicone oil, 3 parts of nano-calcium carbonate, and 4 parts of talc. The corrugated support structure material, component B, contains 80 parts of polyether polyol, 40 parts of castor oil-based polyol, and 60 parts of 4,4-diphenylmethane diisocyanate. The interface reinforcement coating, component A, contains 80 parts of epoxy resin E-44, 25 parts of polyurethane prepolymer, 3 parts of silane coupling agent KH-550, and 1.5 parts of nano-graphene. The interface-reinforced coating component B contains 70 parts unsaturated polyester resin, 35 parts epoxy acrylate, 3 parts silane coupling agent KH-560, and 0.8 parts functionalized carbon nanotubes. The polyurethane prepolymer has a molecular weight of 2500, the polyether polyol has a molecular weight of 3000, and the polycaprolactone diol has a molecular weight of 1200.

[0084] The pulsed electric field parameters were set as follows: electric field strength 0.8 kV / mm, pulse frequency 150 Hz, duty cycle 40%. Higher electric field strength and frequency more effectively promote fiber impregnation in the high-viscosity resin system. The injection pressure for the outer panel material was 1.2 MPa, and the filling speed was 500 g / s; the injection pressure for the inner panel material was 1.1 MPa, and the filling speed was 550 g / s; the injection pressure for the corrugated support structure material was 0.9 MPa. The curing temperatures for each molding cavity were: outer panel 60℃, inner panel 60℃, corrugated support structure center area 60℃, and edge area 50℃. The post-curing temperature was 120℃, with a holding time of 4 hours. The higher post-curing temperature and longer holding time ensured complete curing of the high-filler system.

[0085] The composite hollow board prepared in this embodiment was subjected to performance testing. The measured bending strength of the outer board was 495 MPa, the bending strength of the inner board was 445 MPa, and the impact strength of the outer board was 48 kJ / m. 2 The inner panel impact strength is 68 kJ / m. 2 The overall compression recovery rate is 95.8%, and the shape recovery rate of the corrugated support structure is 99%. This embodiment uses high filler, fiber, and resin content, giving the material excellent strength, stiffness, and resilience. It is suitable for bearing particularly heavy steel coils or for scenarios requiring higher mechanical properties. The high content of epoxy-amine bicore double-walled microcapsules enhances the self-healing ability of the inner plate, and the high content of polycaprolactone diol makes the shape memory performance of the corrugated support structure more significant.

[0086] Example 4 focuses on verifying the impact of the S-shaped design of the corrugated support structure on the cushioning performance. This example uses the same material formulation as Example 1, but the geometric parameters of the corrugated support structure are adjusted. The radius of curvature of the S-shaped surface varies continuously within the range of 15-50 mm, the corrugation height is 35 mm, and the corrugation spacing is 70 mm. The S-shaped design allows the corrugations to have two main deformation stages under pressure: the first stage is the bending of the upper half of the S-shaped curve under pressure, and the second stage is the continued deformation of the lower half of the S-shaped curve. This staged deformation mechanism makes the entire cushioning process smoother and more gradual.

[0087] Dynamic compression tests were conducted on the composite hollow plate prepared in this embodiment using an electronic universal testing machine equipped with a dynamic loading system. The loading rate was 10 mm / min, and the maximum load was 5 kN. Load-displacement curves were recorded. The curves show that the load increases slowly in the initial stage of compression, and the load growth rate accelerates when the displacement reaches 8 mm. This nonlinear response characteristic indicates that the S-shaped corrugated support structure provides a gradual buffering effect. The calculated energy absorption value is 45 J, and the energy absorption density is 0.036 J / mm². 3 The formula for calculating energy absorption density Ea is Ea = W / V; where Ea is the energy absorption density, in J / mm². 3 W represents the total absorbed energy in J; V represents the volume of the corrugated support structure in mm. 3 Cyclic compression tests were conducted, with the same sample subjected to 10 compression-unloading cycles. Each compression was followed by unloading after a displacement of 5 mm. The energy loss for each cycle was recorded. The energy loss for the first cycle was 8%, and for the tenth cycle it was 12%. The gradual increase in energy loss indicates that the material is experiencing some fatigue. However, the energy loss after 10 cycles is still less than 15%, indicating that the material has good cyclic stability.

[0088] Example 5 focuses on verifying the impact of the self-healing system on the service life of the inner panel. This example uses the same material formulation and process parameters as Example 1. After preparation, artificial cracks were created on the inner panel by cutting 10mm long and 1mm deep cracks on the surface using a diamond blade. The cracked sample was then placed in a 60℃ oven for 24 hours for self-healing treatment. The self-healing mechanism is as follows: stress concentration at the crack tip causes the epoxy-amine binuclear double-walled microcapsules at the crack to rupture, releasing the triethylene glycol diepoxyglycerol ether repair agent in the core and the diethylenetriamine curing agent in the outer core. These two agents contact the crack surface and react chemically. Under the action of the amine curing agent, the epoxy groups undergo ring-opening polymerization to form a cross-linked network. The cured product fills the crack and forms chemical bonds with the matrix material, thereby repairing the crack. The 60℃ temperature accelerates the curing reaction, making the repair more complete.

[0089] The crack morphology before and after repair was observed using scanning electron microscopy (SEM). Before repair, the crack surface was rough and had obvious crack openings. After repair, the crack was filled with repair material, and the crack opening width was reduced from the original 50 μm to less than 5 μm, with a repair rate exceeding 90%. Bending strength tests were performed on the repaired specimens, and the measured bending strength was 340 MPa, compared to 385 MPa for the undamaged specimen, representing a strength recovery rate of 88.3%. The strength recovery rate Rs was calculated using the formula Rs = σr / σ0 × 100%; where Rs is the strength recovery rate (%), σr is the bending strength after repair (MPa), and σ0 is the bending strength of the undamaged specimen (MPa). Fatigue life tests were performed on the repaired specimens using a three-point bending fatigue testing machine with a stress ratio R = 0.1, a maximum stress of 200 MPa, and a frequency of 5 Hz. The measured fatigue life of the repaired specimens was 2.8 × 10⁻⁶. 5 After one cycle, the fatigue life of the undamaged specimen was 3.5 × 10⁻⁶. 5 After one cycle, the fatigue life recovery rate was 80%, which indicates that the self-healing system can significantly extend the service life of the inner plate after being subjected to micro-damage. For repeatedly used steel coil packaging materials, the self-healing function can greatly reduce maintenance costs.

[0090] Comparative Example 1 differs from Example 1 in that no toughening components were added to the formulations of the outer and inner panels. Silicon carbide micropowder was not added to the outer panel material, and carboxyl-terminated polybutadiene rubber toughening agent and maleic anhydride-grafted polypropylene synergist were not added to the inner panel material. The remaining formulations and process parameters were the same as in Example 1.

[0091] The composite hollow plate prepared in Example 1 was subjected to performance tests. The bending strength of the outer plate was 440 MPa, the bending strength of the inner plate was 410 MPa, and the impact strength of the outer plate was 28 kJ / m. 2The inner panel impact strength is 35 kJ / m. 2 The overall compression recovery rate was 85.5%, and the shape recovery rate of the corrugated support structure was 93%. The test results show that although the bending strength was slightly improved, the impact strength was significantly reduced, and the recovery performance was also decreased. This indicates that the addition of toughening components is crucial for improving the toughness and elastic deformation capacity of the material.

[0092] Comparative Example 2 differs from Example 1 in that the epoxy-amine bicore double-walled microcapsule self-healing system was not added to the inner plate material; the rest of the formulation and process parameters are the same as in Example 1.

[0093] The inner panel of the composite hollow plate prepared in Example 2 underwent the same artificial pre-crack and repair treatment as in Example 5. SEM observation after repair showed that the crack morphology remained essentially unchanged, with the crack opening width still around 48 μm, indicating a repair rate close to 0%. Bending strength testing was performed on the repaired sample, yielding a bending strength of 190 MPa, compared to 380 MPa for the undamaged sample, representing a strength recovery rate of only 50%. Fatigue life testing was conducted on the repaired sample, yielding a fatigue life of 8.5 × 10⁻⁶. 4 After one cycle, the fatigue life of the undamaged specimen was 3.4 × 10⁻⁶. 5 After one cycle, the fatigue life recovery rate was only 25%, which fully demonstrates that the epoxy-amine dual-core double-walled microcapsule self-healing system has a significant effect on improving the damage tolerance of the inner plate and extending its service life.

[0094] Comparative Example 3 differs from Example 1 in that polycaprolactone diol shape memory enhancer was not added to the corrugated support structure material; the rest of the formulation and process parameters are the same as in Example 1.

[0095] The composite hollow board corrugated support structure prepared in Comparative Example 3 was subjected to the same shape memory performance test as in Example 1. It was heated to 60°C to soften it and then deformed by applying external force. After cooling to room temperature while maintaining the deformed state, it was reheated to 60°C. It was observed that the shape recovery of the corrugated support structure was very slow and incomplete. After 60 minutes, the shape recovery rate was only 65%, compared with the 98% shape recovery rate of Example 1, showing a significant difference. This indicates that polycaprolactone diol shape memory reinforcing agent is the key component for achieving good shape memory characteristics of the corrugated support structure. When the composite hollow board is deformed by compression in steel coil packaging applications, the shape memory characteristics can help the corrugated support structure quickly recover its original shape, ensuring the reusability of the packaging material.

[0096] Comparative Example 4 differs from Example 1 in that it does not use a pulsed electric field assisted molding process. No pulsed electric field is applied during the injection molding process. The rest of the formulation and process parameters are the same as those in Example 1.

[0097] The interfacial bonding strength of the composite hollow board prepared in Comparative Example 4 was tested using the peel test method according to GB / T 2791-1995 "Adhesives T Peel Strength Test Method Flexible Materials to Flexible Materials". Peel samples were prepared at the interface between the outer board and the corrugated support structure. The peel speed was 100 mm / min, and the interfacial peel strength was measured to be 2.8 kN / m. The same test was performed on the sample prepared in Example 1, and the interfacial peel strength was measured to be 4.5 kN / m. The interfacial bonding strength of Comparative Example 4 was 38% lower than that of Example 1. This indicates that the application of a pulsed electric field can significantly improve the resin wetting of the fiber and the interfacial bonding. Under the action of the pulsed electric field, the dipole orientation of the resin molecules is conducive to the resin penetrating into the fiber bundle. The electric field can also promote the chemical reaction at the interface, thereby improving the interfacial bonding strength. Interlaminar shear strength tests were conducted on both types of specimens according to GB / T3357-2009 "Test Method for Interlaminar Shear Strength of Fiber Reinforced Plastics". The specimen size was 20mm × 10mm × plate thickness, with a span of 10mm and a loading speed of 1mm / min. The interlaminar shear strength of Comparative Example 4 was 28MPa, while that of Example 1 was 42MPa. The interlaminar shear strength of Comparative Example 4 was 33% lower than that of Example 1.

[0098] Comparative Example 5 differs from Example 1 in that the corrugated support structure uses a traditional straight-line design instead of an S-shaped design. The corrugated support structure is a simple Z-shape, with a vertical section length of 40 mm and a horizontal section length of 10 mm. The remaining formulation and process parameters are the same as in Example 1. The composite hollow plate prepared in Comparative Example 5 underwent dynamic compression testing under the same conditions as in Example 4. The recorded load-displacement curve showed that the load increased approximately linearly with displacement, without exhibiting the staged deformation characteristics seen in Example 4. The calculated energy absorption value was 28 J, and the energy absorption density was 0.022 J / mm². 3 Compared to 0.036 J / mm in Example 4 3 The energy loss was reduced by 39%. Cyclic compression tests were conducted, and the energy loss was 15% in the first cycle and 28% in the tenth cycle. The energy loss after the tenth cycle was significantly higher than the 12% in Example 4, indicating that the fatigue stability of the straight corrugated support structure is poor. This is because the S-shaped curved surface distributes stress more evenly under load, avoiding stress concentration at the turning points of the straight structure. The progressive deformation mechanism of the S-shaped design also makes the buffering effect smoother and can absorb impact energy more effectively.

[0099] To comprehensively evaluate the overall performance of each embodiment and comparative example, a systematic comparative experiment was conducted. Test indicators included the bending strength of the outer plate, the bending strength of the inner plate, the impact strength of the outer plate, the impact strength of the inner plate, the overall compression rebound rate, the interfacial peel strength, the energy absorption density, and the shape recovery rate. The bending strength of the outer and inner plates was tested according to GB / T 1449-2005 "Test Method for Bending Properties of Fiber Reinforced Plastics". The specimen size was 80mm × 10mm × plate thickness, with a span of 64mm. The loading speed was 2mm / min, using a three-point bending loading method. The testing machine had an accuracy class of 0.5. Strain gauges were attached to the bottom surface of the specimen at mid-span to monitor strain, and the bending strength was calculated based on the load-displacement curve. The impact strength of the outer and inner panels was tested according to GB / T 1043-2008 "Determination of Impact Properties of Simply Supported Beams in Plastics". The sample size was 80mm × 10mm × plate thickness, with a notch depth of 2mm and a notch tip radius of 0.25mm. A pendulum impact testing machine was used, with a pendulum energy of 5J, a test temperature of 23±2℃, and a relative humidity of 50±10%. The impact strength was calculated based on the energy consumed by the impact to break the sample. The overall compression rebound rate was tested using a compression testing machine. The sample size was 100mm × 100mm × plate thickness. A pressure of 1MPa was applied for 10 seconds, and the compression deformation was measured with a dial indicator. After unloading, the residual deformation was measured after 60 seconds, and the rebound rate was calculated according to the formula. The interfacial peel strength was tested according to GB / T 2791-1995 "Test Method for Peel Strength of Adhesives - Flexible Materials to Flexible Materials". Peel samples were prepared at the interface between the outer panel and the corrugated support structure. The sample width was 25mm, the peel speed was 100mm / min, and the average load during the peel process was recorded. Energy absorption density testing employed a universal electronic testing machine for dynamic compression. The sample size was 100mm × 100mm × plate thickness, the loading rate was 10mm / min, and the maximum load was 5kN. Load-displacement curves were recorded, and the area under the curve was calculated to obtain the absorbed energy. Dividing this area by the sample volume yielded the energy absorption density. For shape recovery testing, the corrugated support structure was heated to 60℃ to soften it, deformed by external force, cooled and fixed, and then reheated to 60℃. The geometric dimensions before and after deformation were measured to calculate the recovery rate.

[0100] The results of the comparative experiment are shown in Table 1. Figure 3 , Figure 4 , Figure 5As shown in Table 1, which compares the comprehensive performance of each embodiment and comparative example, it can be seen from Table 1 that the impact strength and resilience of Comparative Example 1 are significantly reduced due to the lack of toughening components. The impact strength of the outer plate is reduced by 33% compared to Example 1, and the impact strength of the inner plate is reduced by 40% compared to Example 1. This fully demonstrates that toughening components play a key role in improving the toughness and impact resistance of materials. Silicon carbide micropowder, as a hard filler, can improve toughness through crack deflection while improving wear resistance. Carboxyl-terminated polybutadiene rubber, as an elastomer phase, is dispersed in the brittle resin matrix. Under impact load, the rubber phase undergoes shear yielding and absorbs energy. Maleic anhydride-grafted polypropylene improves the interfacial bonding between the rubber phase and the resin phase, making the toughening effect more significant. Comparative Example 4, without the use of pulsed electric field assisted process, showed a 38% reduction in interfacial peel strength compared to Example 1. This indicates that the application of pulsed electric field is crucial for improving interfacial bonding. During reaction injection molding, the mechanism of pulsed electric field includes the following aspects: First, the electric field force causes the resin molecules to align their dipoles and align along the direction of the electric field, enhancing the wetting ability of the resin molecules on the fiber surface. Second, the electric field can reduce the apparent viscosity of the resin, making it easier for the resin to penetrate into the fiber bundle. Third, the electric field can promote the chemical reaction between the silane coupling agent at the interface and the fiber and resin. Finally, the Joule heating effect generated by the pulsed electric field also helps to accelerate the curing reaction. The synergy of multiple mechanisms significantly improves the interfacial bonding strength. Comparative Example 5, due to the adoption of a straight-line corrugated support structure, reduced the energy absorption density by 39% compared to Example 4. The advantage of the S-shaped corrugated design lies in its unique geometry, which provides a progressive deformation mechanism. When subjected to compressive load, the S-shaped curve first undergoes bending deformation at the part with greater curvature. As the load increases, the deformation gradually extends to the entire S-shaped curve. This staged deformation makes the stress-strain curve present a plateau region, which can maintain relatively stable stress within a large deformation range, thereby achieving efficient energy absorption. In contrast, the straight-line corrugated structure has stress concentration at the turning point, which is prone to local damage and has poor energy absorption capacity.

[0101] Table 1. Comparison of overall performance of each embodiment and comparative example.

[0102]

[0103] The data analysis in Table 1 shows that the three-dimensional cross-linked network formed by epoxy resin and hardener provides basic stiffness, toughening components improve toughness and impact resistance, and fiber reinforcement provides a load-bearing skeleton. Only a reasonable ratio of multiple components can achieve a balanced optimization of comprehensive performance.

[0104] The addition of an epoxy-amine bicore double-walled microcapsule self-healing system to the inner panel material significantly improved the material's damage tolerance. The experimental results of Comparative Example 2 showed that the inner panel without the self-healing system had a strength recovery rate of only 50% after cracking, while the strength recovery rate of Example 5 with the addition of the self-healing system reached 88.3%, and the fatigue life recovery rate reached 80%. The self-healing mechanism is that the microcapsules rupture at the crack to release the repair agent and curing agent. The polymer generated by the reaction of the two fills the crack and bonds with the matrix, thereby achieving in-situ repair of the crack. This self-healing ability is of great significance for extending the service life of repeatedly used steel coil packaging materials.

[0105] The addition of polycaprolactone diol shape memory enhancer to the corrugated support structure material gives it excellent shape memory properties. The shape recovery rate of Comparative Example 3 is only 65%, while the shape recovery rates of Examples 1, 4, and 5 all reach 98%. The working principle of the shape memory polymer is that the crystalline phase of polycaprolactone diol melts at a lower temperature, and the amorphous phase can be deformed under external force. After cooling, the crystalline phase reforms into a fixed deformed shape. When heated again, the crystalline phase melts again, and the amorphous phase recovers to its original shape through entropy elasticity. This shape memory property ensures that the corrugated support structure can automatically recover after being deformed by compression, thus guaranteeing the reusability of the hollow board in the composite material.

[0106] Pulsed electric field assisted reaction injection molding process has a significant effect on improving interfacial bonding strength. Comparative Example 4, which did not use the pulsed electric field assisted process, had an interfacial peel strength of only 2.8 kN / m. However, Examples 1, 4, and 5, which used the pulsed electric field assisted process, all achieved an interfacial peel strength of 4.5 kN / m, an increase of 60%. The pulsed electric field significantly improved the interfacial bonding between the fiber and the resin matrix through the synergistic effect of multiple mechanisms, such as promoting the dipole orientation of resin molecules, reducing apparent viscosity, and accelerating interfacial chemical reactions. Good interfacial bonding is a key factor in ensuring the overall mechanical properties of composite materials.

[0107] Compared to the traditional straight-line design, the S-shaped design of the corrugated support structure has superior energy absorption capacity and fatigue stability. Comparative Example 5, which uses a straight-line corrugated structure, has an energy absorption density of only 0.022 J / mm². 3 In Example 4, the S-shaped corrugated energy absorption density reached 0.036 J / mm². 3 The S-shaped corrugations, with their progressive deformation mechanism and uniform stress distribution, have improved by 64%, enabling them to absorb impact energy more effectively. This provides excellent protection against various impact loads that steel coil packaging may experience during transportation.

[0108] Figure 3This system comparison includes eight key performance indicators. The outer and inner panel bending strengths reflect the material's ability to resist bending loads, which is crucial for the composite hollow board to withstand bending stress without fracture during steel coil stacking and handling. The outer and inner panel impact strengths reflect the material's toughness against impact damage, which is crucial for absorbing impact energy without brittle cracking when subjected to sudden impact loads such as falling steel coils or transport bumps. The overall compression rebound rate reflects the material's elastic recovery ability after compression, which is crucial for the composite hollow board to recover its original thickness and maintain cushioning performance after long-term bearing of steel coil weight. The interfacial peel strength reflects the strength of the interfacial bond between the outer and inner panels and the corrugated support structure, which is crucial for preventing delamination failure of the composite hollow board during use. The energy absorption density reflects the material's ability to absorb impact energy per unit volume during compression, which is crucial for the effectiveness of cushioning protection. The shape recovery rate reflects the material's shape memory properties, which is crucial for reusability.

[0109] Bending strength was tested using the three-point bending method according to GB / T 1449-2005. A specimen with dimensions of 80mm × 10mm × plate thickness was placed on a support with a span of 64mm. A concentrated load was applied at the midpoint at a loading speed of 2mm / min. The maximum load at which the specimen fractured was recorded, and the bending strength was calculated. Impact strength was tested using a simply supported beam impact test according to GB / T 1043-2008. A 2mm deep V-notch was pre-made in the middle of the specimen. A pendulum impacted the back of the notch, and the energy consumed to break the specimen was recorded and divided by the cross-sectional area at the notch to obtain the impact strength. Compression rebound rate was tested using an electronic universal testing machine. A 5kN compressive load was applied to the entire composite hollow plate, compressing it to 50% of its original thickness. The compression was maintained for 30 seconds, then unloaded. After the specimen rebounded freely for 5 minutes, its thickness was measured. The rebound rate is the ratio of the rebounded thickness to the original thickness. The interfacial peel strength was tested according to GB / T 2791-1995 standard. A 25mm wide peel specimen was prepared at the interface between the outer plate and the corrugated support structure. The free ends of the outer plate and the corrugated support structure were clamped in the upper and lower fixtures of a tensile testing machine, respectively. T-shaped peeling was performed at a speed of 100mm / min. The average load during the peeling process was recorded and divided by the specimen width to obtain the peel strength. Energy absorption density was obtained through dynamic compression testing. The specimen was compressed at a rate of 10mm / min, and the load-displacement curve was recorded. The curve was integrated to calculate the total energy absorbed during the compression process, and then divided by the specimen volume to obtain the energy absorption density.

[0110] Figure 3The comparison of bending properties shows that the bending strength of the outer panel in Example 2 is 365 MPa and the bending strength of the inner panel is 325 MPa. As can be seen from the figure, the bending strength of Comparative Example 1 is slightly higher (440 MPa for the outer panel and 410 MPa for the inner panel). This is because Comparative Example 1 did not add any toughening components, making the material more brittle and harder, thus resulting in a higher bending strength value. However, this high strength comes at the cost of sacrificing toughness; it is a brittle strength. Example 3 uses the upper limit of the formulation, achieving a bending strength of 495 MPa for the outer panel and 445 MPa for the inner panel, the highest values ​​among all samples. This demonstrates that a high-content formulation can achieve high strength while maintaining excellent toughness.

[0111] Figure 3 The comparison of impact performance revealed more significant differences. The impact strength of the outer panels in Examples 1, 4, and 5 was all 42 kJ / m. 2 The impact strength of both inner and outer panels is 58 kJ / m. 2 The impact strength of the outer panel in Comparative Example 1 is only 28 kJ / m². 2 The inner panel has an impact strength of only 35 kJ / m. 2 Compared to Example 1, the impact strength was reduced by 33% and 40%, respectively. This demonstrates that the toughening component is crucial for improving the material's toughness. Its mechanism of action is that silicon carbide micropowder, as rigid particles, generates crack deflection, pinning, and bridging effects along the crack propagation path, increasing crack propagation resistance. Carboxyl-terminated polybutadiene rubber, as an elastomer phase, is dispersed in the brittle resin matrix to form an island structure. Upon impact, the rubber phase undergoes crazing and voiding, consuming a large amount of impact energy. Maleic anhydride-grafted polypropylene, through the reaction of its maleic anhydride groups with epoxy groups and the compatibility of polypropylene segments with rubber, enhances the interfacial compatibility between the toughening agent and the matrix, allowing the toughening effect to be fully realized. The highest impact strength of the outer plate in Example 3 was 48 kJ / m. 2 Inner plate 68kJ / m 2 This demonstrates that formulations with high toughening component content have a more significant toughening effect.

[0112] Figure 3The biaxial comparison of rebound rate and interfacial strength shows that the compression rebound rate of Examples 1, 4, and 5 is 93.5%, and the interfacial peel strength is 4.5 kN / m. In contrast, the compression rebound rate of Comparative Example 1 is 85.5%, a decrease of 8.6%, and the interfacial peel strength of Comparative Example 4 is only 2.8 kN / m, a decrease of 37.8%. The decrease in the rebound rate of Comparative Example 1 is due to the lack of toughening components, which leads to more irreversible plastic deformation and microcracks in the material during compression. The significant decrease in the interfacial strength of Comparative Example 4 directly proves the key role of the pulsed electric field assisted process. This process promotes the orientation of resin molecular dipoles along the electric field direction through the pulsed electric field, thereby reducing the apparent viscosity of the system and improving fluidity. At the same time, the electric field force drives charged ions and polar molecules to migrate to the fiber surface, accelerating the chemical reaction at the interface, reducing the wetting angle of the resin to the fiber, increasing the penetration depth, and ultimately forming a denser transition layer and more chemical bonding points in the interfacial region. Example 3 showed a rebound rate of up to 95.8% and an interfacial strength of up to 5.2 kN / m, demonstrating that the high-content formulation also has advantages in these two properties.

[0113] Figure 3 The biaxial comparison of energy absorption and shape recovery presents the most dramatic contrast. Comparative Example 5 has an energy absorption density of only 22 mJ / mm². 3 It is much lower than the 36 mJ / mm of Example 4. 3 The energy absorption capacity was reduced by 38.9%. This is because Comparative Example 5 used a linear corrugated design, whose load-displacement curve showed an approximately linear increase. Stress concentrated at the corners of the corrugations, leading to localized failure. In contrast, the S-shaped corrugated design of Example 4 resulted in a distinct two-stage progressive increase in the load-displacement curve. In the first stage, the upper half of the S-shaped curve, with a displacement of 0-8mm, gradually absorbed energy through compression and bending. In the second stage, the lower half of the S-shaped curve, with a displacement of 8-20mm, continued to deform and absorb more energy. This staged deformation mechanism resulted in a more uniform stress distribution, preventing premature localized failure and significantly improving energy absorption capacity. The shape recovery rate of Comparative Example 3 was only 65%, far lower than the 98% of Example 1, a reduction of 33.7%. The reasons for this difference have been analyzed in detail above. Although Example 2 used the lower limit of the formulation, its energy absorption density was 30 mJ / mm². 3 The shape recovery rate was 95%, which is still significantly better than all comparative examples, proving that the formulation range of the present invention has good adaptability.

[0114] Figure 3Through a systematic comparison of the four sub-figures, it is clearly shown that the five embodiments exhibit balanced and excellent performance across various aspects, while the five comparative examples each have obvious performance shortcomings. Comparative Example 1, although slightly higher in flexural strength, shows a significant decrease in impact strength and springback rate, demonstrating that simply pursuing high strength without toughening components leads to high brittleness and poor toughness. Comparative Example 2 is close to the embodiments in most indicators, but its lack of self-healing ability will lead to cumulative damage that cannot be repaired and eventual failure over long-term use. Comparative Example 3's significant disadvantage in shape recovery rate renders it unusable. The substantial decrease in interface strength in Comparative Example 4 demonstrates that the pulsed electric field process is crucial for ensuring the integrity of the multilayer structure. Comparative Example 5 exhibits the worst energy absorption capacity, indicating that the corrugated structure design has a decisive impact on buffering performance. In summary, Figure 3 This invention demonstrates that through the synergistic effect of toughening component optimization, introduction of a self-healing system, addition of shape memory enhancer, pulsed electric field process, and corrugated structure design, it achieves multiple performance goals of high strength, high toughness, high resilience, strong interface, high energy absorption, and excellent shape memory.

[0115] Figure 4 The shape recovery rate refers to the degree to which a material can recover its original shape after being deformed under pressure and then subjected to heat treatment. The higher the value, the better the shape memory performance of the material. For composite hollow boards used in steel coil packaging, this indicator is directly related to whether the corrugated support structure can recover its original shape after being compressed and deformed by the weight of the steel coil, thus enabling reuse.

[0116] The corrugated support structures prepared in Example 1 and Comparative Example 3 were heated to 60°C to soften them, deformed by applying external force, and kept in this deformed state while cooling to room temperature to fix their shape. They were then reheated to 60°C and held for 60 minutes. The degree to which they returned to their original shape was measured, and the shape recovery rate was calculated. Example 1 contained polycaprolactone diol shape memory enhancer. The polycaprolactone segments with a molecular weight of 800-1200 have a crystalline phase melting temperature of approximately 60°C when heated. After melting, the amorphous phase segments rely on entropic elasticity to drive the material to return to its original shape. In contrast, Comparative Example 3, without this component, relied solely on the elastic recovery of the unsaturated polyester resin and polyurethane elastomer, resulting in a slow and incomplete recovery process.

[0117] Figure 4 The bar chart shows that the shape recovery rate of Example 1 reached 98%, while that of Comparative Example 3 was only 65%. In comparison, Example 1 improved by 51%, indicating that the corrugated support structure of Example 1 can almost completely recover its original shape, while more than one-third of the deformation of Comparative Example 3 cannot be recovered. Figure 4The dynamic recovery curves further revealed the differences in the recovery process: Example 1 achieved a shape recovery rate of approximately 85% after 10 minutes of heating and 98% after 30 minutes, while Comparative Example 3 only achieved a shape recovery rate of approximately 50% after 30 minutes of heating, and even after 60 minutes of heating, it could only recover to 65%, with the curve showing a continuously slow recovery speed. Polycaprolactone diol shape memory enhancer is a key component for achieving rapid and efficient recovery of the corrugated support structure. Its working principle is that the crystalline phase of the polycaprolactone chain undergoes a reversible melt transition upon heating. This phase transition process provides a clear thermal response switching temperature for the shape memory behavior, allowing the material to fix its deformed shape below this temperature and rapidly return to its original state above it. Although Comparative Example 3 also contains polyurethane elastomer, this elastomer has a wide glass transition temperature and no clear phase transition point, resulting in a slow and insufficient recovery process. The excellent shape memory properties of Example 1 ensure that the composite hollow board can quickly and automatically recover its original shape after being compressed and deformed by several tons of steel coils in steel coil packaging applications. This allows for repeated use without the loss of cushioning performance due to cumulative deformation, which has important practical value for reducing packaging material costs and improving logistics efficiency.

[0118] Figure 5The stress-strain curve is a fundamental characterization of the mechanical properties of materials. The horizontal axis, strain, represents the relative deformation of the material, while the vertical axis, stress, represents the force per unit area. The shape of the curve reflects the mechanical behavior of the material. In Example 1, the solid blue line indicates that the stress initially increases approximately linearly with strain, reflecting the elastic deformation stage. Subsequently, the slope of the curve gradually decreases, entering the yielding and plastic deformation stages. The large area under the curve indicates that the material can withstand significant deformation and absorb more energy before fracture, which is a typical characteristic of ductile materials. In Comparative Example 1, the dashed red line shows a steeper initial slope, indicating a higher elastic modulus and harder material. However, it quickly fractures after reaching maximum stress, and the area under the curve is significantly smaller than that of Example 1, which is a typical characteristic of brittle materials. The difference between the two curves directly reflects the effect of the toughening components. The microscopic mechanism is as follows: Silicon carbide micropowder, as hard and rigid particles, is uniformly dispersed in the resin matrix. When crack propagation encounters these particles, the crack must bypass the particles or cause the particles to debond, which changes the crack propagation path from a straight line to a tortuous one, increasing the energy required for crack propagation. The carboxyl-terminated polybutadiene rubber has good molecular chain flexibility, forming micron-sized rubber phase particles in the resin matrix. When the material is impacted, the stress concentration at the crack tip first causes crazing in the rubber phase, i.e., a large number of oriented microfibers and voids. The formation and propagation of these crazing consume a lot of energy. At the same time, the bridging effect of the rubber phase hinders crack propagation. Maleic anhydride-grafted polypropylene is an interfacial compatibilizer. Its maleic anhydride groups can react with the epoxy groups of epoxy resin to form covalent bonds, and the polypropylene segments have good compatibility with the rubber phase. This structure makes it connect the rubber toughening agent to the resin matrix like a molecular bridge, ensuring that stress can be effectively transferred to the rubber phase so that the toughening mechanism can play its full role. Example 1 transforms the brittle fracture mode of Comparative Example 1 into a ductile fracture mode through the synergistic effect of these three toughening components, thereby significantly improving the impact strength and energy absorption capacity of the material.

[0119] Figure 5The crack width-time curve reveals the dynamic repair process of the self-healing system. In Example 5, the solid blue dot curve shows that the crack width rapidly decreases exponentially over time from an initial 50 μm, decreasing to approximately 18 μm at 6 hours, approximately 7 μm at 12 hours, and below approximately 5 μm at 24 hours, indicating almost complete crack closure. In Comparative Example 2, the dashed red square curve shows that the crack width remained around 50 μm throughout the 24-hour observation period, indicating no repair occurred. The repair mechanism of Example 5 is based on an intelligent responsive release system of epoxy-amine bicore double-walled microcapsules: these microcapsules are prepared using interfacial polymerization, with a core encapsulating a triethylene glycol diglycidyl ether repair agent and an outer core encapsulating a diethylenetriamine curing agent. The inner wall is a polyurethane-urea-formaldehyde resin composite material with a thickness of approximately 2-3 μm, and the outer wall is a polyurea material with a thickness of approximately 1-2 μm. The total diameter of the microcapsules is approximately 50-200 μm. When a material is subjected to external force and cracks develop, the high stress concentration area at the crack tip causes the microcapsule wall material located along the crack path to rupture. First, the outer wall ruptures, releasing the curing agent diethylenetriamine, followed by the inner wall ruptures, releasing the repair agent diethylene glycol diglycidyl ether. The two react and mix within the crack pores. The epoxy groups in the repair agent molecule and the amino groups in the curing agent molecule rapidly undergo ring-opening polymerization. One amino group reacts with an epoxy group to form a hydroxylamine. The secondary amino group in the hydroxylamine can further react with another epoxy group to form a tertiary amine, forming a three-dimensional cross-linked network polymer. This polymer gradually fills the crack and forms chemical bonds with the surrounding matrix resin, thus achieving in-situ automatic repair of the crack. The dual-core, dual-wall structure design is crucial: if the repair agent and curing agent are stored in the same space, they will pre-react inside the microcapsule, causing the repair function to fail. The dual-core design ensures that they are stored separately, only mixing and reacting when the microcapsule ruptures at the crack. The dual-wall structure provides sufficient mechanical strength and chemical stability, ensuring that the microcapsule does not rupture and fail during material preparation, while simultaneously allowing timely release under crack stress. Figure 5-2 The curve exhibits an exponential decay characteristic. This is because the high concentrations of the repair agent and curing agent, the large crack width, and the rapid reaction rate result in a significant repair effect in the initial stage of the repair reaction. As the reaction progresses, the concentration decreases, the crack width narrows, and the reaction rate slows down, but the crack can still be closed to a high degree in the end. In Comparative Example 2, due to the lack of a self-healing system, cracks persist once they form and may even continue to propagate under stress, leading to continuous deterioration of material properties until eventual failure. The self-healing capability of Example 5 can not only repair macroscopically visible cracks, but more importantly, it can repair a large number of microcracks invisible to the naked eye in the early stages of material use. If these microcracks are not repaired, they will gradually connect and expand into macroscopic cracks. Therefore, the self-healing system effectively extends the lifespan of the material from damage initiation to eventual failure.

[0120] Figure 5The impregnation depth-time curves illustrate the promoting effect of the pulsed electric field assisted process on the fiber impregnation process. The solid purple line in Example 1 shows that the impregnation depth increases rapidly with time, reaching approximately 3.5 mm at 3 seconds, approximately 5 mm at 6 seconds, and approximately 6.3 mm at 10 seconds, with the growth rate following a power function law. The dashed red line in Comparative Example 4 shows that the impregnation depth increases significantly and slowly, reaching only approximately 2.1 mm at 3 seconds, approximately 3 mm at 6 seconds, and approximately 3.9 mm at 10 seconds. The difference in fiber impregnation depth directly determines the quality of interfacial bonding. A greater impregnation depth indicates that the resin penetrates deeper into the fiber bundle, resulting in a larger contact area between the fiber and the resin, and a stronger interfacial bond. The mechanism of action of the pulsed electric field assisted process in Example 1 includes several synergistic effects: First, the dipole orientation effect. Resin molecules such as epoxy resin and polyurethane prepolymer contain polar groups that form molecular dipoles. Under the action of the pulsed electric field, these dipoles are oriented along the direction of the electric field, reducing the intermolecular interaction forces, decreasing the apparent viscosity of the system, enhancing resin fluidity, and making it easier to penetrate into the narrow gaps of the fiber bundle. Second, the electrophoretic effect. Charged ions and polar molecules in the resin system migrate directionally under the drive of the electric field and accumulate on the fiber surface. The increased concentration of these active species on the fiber surface accelerates the interfacial chemical reaction. Third, the electric field enhances the wetting effect. The electric field changes the charge distribution at the solid-liquid interface, reduces the contact angle between the resin and the fiber, improves wettability, and makes the resin easier to spread on the fiber surface. Fourth, the thermal effect. The pulsed electric field generates Joule heating in the resin, and the localized temperature rise further reduces viscosity and accelerates the chemical reaction. As a result of the synergistic effect of these factors, the resin of Example 1 can penetrate the fiber bundle more deeply in a shorter time, forming more chemical bonding points at the fiber-resin interface. For example, the siloxane groups of silane coupling agents KH-550 and KH-560 form Si-O-Si covalent bonds with the hydroxyl groups on the fiber surface, while the organic groups react with the resin matrix to form a thicker and denser transition layer at the interface. This transition layer can effectively transfer stress and prevent the propagation of interfacial cracks. In Comparative Example 4, no pulsed electric field process was used. The resin impregnation of the fiber mainly relied on capillary force and pressure, which was slow and insufficient. Dry fiber or insufficient resin content often existed inside the fiber bundle, especially in the central region. These areas became stress concentration points and the starting points of interfacial failure, resulting in a significant reduction in interfacial peel strength. Figure 5-3 The difference between the two curves quantitatively demonstrates the degree of interface wetting improvement brought about by the pulsed electric field process. This improvement is ultimately reflected in the interface peel strength of Example 1 (4.5 kN / m) being 60.7% higher than that of Comparative Example 4 (2.8 kN / m).

[0121] Figure 5The toughening components alter the microscopic failure mode of the material. In Comparative Example 1, brittle fracture is characterized by rapid crack propagation, low energy absorption, and low impact strength, while in Example 1, ductile fracture is characterized by high crack propagation resistance, high energy absorption, and high impact strength. The microscopic mechanism of this transformation is the result of the synergistic effect of crack deflection by rigid particles, energy absorption by crimping of the elastomeric phase, and stress transfer by the interfacial compatibilizer. Figure 5-2 The self-healing system achieves the material's self-repair capability by responding to crack damage. In Comparative Example 2, the crack persists and expands, with a low strength recovery rate and short fatigue life. In contrast, the crack in Example 5 automatically closes and recovers strength, with a high strength recovery rate and long fatigue life. The microscopic mechanism of this difference is the result of stress-response rupture release of the dual-core double-walled microcapsules and in-situ polymerization and filling repair of the repair agent and curing agent. Figure 5-3 The pulsed electric field process optimizes the fiber impregnation quality during the preparation process through the synergistic effect of multiple physical and chemical effects. Comparative Example 4 showed insufficient impregnation and weak interfacial bonding, resulting in low interfacial peel strength. In contrast, Example 1 showed deep impregnation, strong interfacial bonding, and high interfacial peel strength. This is a comprehensive result of electric field-induced dipole orientation to reduce viscosity, electrophoretic enrichment to promote reaction, enhanced wetting to improve spreading, and local heating to accelerate curing.

[0122] Figure 5 The three mechanisms demonstrated are not isolated but interconnected, forming a synergistic effect. The toughening component improves the material's toughness and reduces the tendency for brittle cracking, creating conditions for the self-healing system to function. If the material is too brittle, cracks will quickly penetrate the entire cross-section, causing material fracture, and the self-healing system will not have time to function. The improved interfacial bonding of the pulsed electric field process ensures that the layers of material work together to prevent delamination, providing a foundation for the overall structure to perform toughening and self-healing functions. The progressive deformation mechanism of the S-shaped corrugation design makes stress distribution more uniform, avoiding premature local failure. This extends the response time of the self-healing system and the effectiveness of the toughening component. The composite hollow board was systematically optimized from three levels: the design of the toughening component and the self-healing system to optimize the intrinsic properties of the material; the design of the pulsed electric field process to optimize manufacturing process quality; and the structural geometry design. This achieved multiple performance goals, including high strength, high toughness, self-healing, strong interface, and excellent energy absorption, providing a complete technical solution for the long life, high reliability, and reusability of steel coil packaging materials.

[0123] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite hollow plate, characterized in that, It consists of an outer panel and an inner panel, with the outer panel being 2-10mm thick and the inner panel being 2-8mm thick; several corrugated support structures connect the outer panel and the inner panel; there is a cavity between adjacent corrugated support structures; The outer panel is composed of the following components in parts by weight: Matrix resin: 100-160 parts of epoxy resin E-51; hardener: 20-30 parts of 4,4-diaminodiphenylmethane; wear-resistant reinforcing agent: 5-10 parts of nano-silica, 8-15 parts of silicon carbide micro powder; coupling agent: 1-3 parts of silane coupling agent KH-560; reinforcing fiber: 50-100 parts of chopped glass fiber mat. The inner plate is composed of the following components in parts by weight: Matrix resin: 100 parts vinyl ester resin, 70-90 parts epoxy acrylate; Linear polymer network: 20-30 parts polyurethane prepolymer; Curing system: 3-5 parts benzoyl peroxide, 0.5-1.5 parts dimethylaniline; Toughening agent: 15-25 parts carboxyl-terminated polybutadiene rubber; Synergistic additive: 4-8 parts maleic anhydride-grafted polypropylene; Self-healing system: 8-15 parts epoxy-amine bicore double-walled microcapsules; Nano-reinforcing agent: 3-6 parts organically modified montmorillonite; Reinforcing fiber: 80-120 parts continuous glass fiber mat; The corrugated support structure is composed of the following components in parts by weight: First network resin: 100 parts of phthalic unsaturated polyester resin; Second network polyol component: 60-80 parts of polyether polyol, 30-40 parts of castor oil-based polyol; Second network isocyanate component: 40-60 parts of 4,4-diphenylmethane diisocyanate; Reinforcing fiber: 60-90 parts of chopped glass fiber, 40-60 parts of glass fiber nonwoven fabric; Crosslinking agent: 2-4 parts of divinylbenzene; Curing system: 3-5 parts of cyclohexanone peroxide, 0.4-1.0 parts of dibutyltin dilaurate; Shape memory reinforcing agent: 5-10 parts of polycaprolactone diol; Foaming agent: 1-2 parts of azodicarbonamide, 3-5 parts of a composite system of sodium bicarbonate and citric acid; Foaming stabilizer: 0.5-1.5 parts of silicone oil; Nucleating agent: 1-3 parts of nano-calcium carbonate, 2-4 parts of talc. The preparation process of the epoxy-amine bicore double-wall microcapsules includes: using triethylene glycol diepoxyglycerol ether as the core repair agent and diethylenetriamine as the outer core curing agent, and preparing them by interfacial polymerization. The inner wall is a polyurethane-urea-formaldehyde resin composite wall material, and the outer wall is a polyurea wall material. The preparation process of the organically modified montmorillonite includes: dispersing sodium montmorillonite in water at 80-90℃, adding octadecyltrimethylammonium chloride, stirring and reacting at 60-70℃ for 2-4 hours, and washing until no Cl is found. - After ionization, drying and grinding were performed to obtain organically modified montmorillonite; The polyurethane prepolymer is castor oil type with a molecular weight of 1500-2500, the polyether polyol has a molecular weight of 2000-3000, and the polycaprolactone diol has a molecular weight of 800-1200.

2. The preparation process of the composite hollow plate as described in claim 1, characterized in that, Includes the following steps: S1: Prepare an interface-reinforced coating. Prepare interface-reinforced coating component A and component B respectively. Component A is used for fiber pretreatment of the outer and inner panels, and component B is used for interface reinforcement of the corrugated support structure surface. S2: Prepare a three-cavity partitioned mold, including an outer plate forming cavity, an inner plate forming cavity and a corrugated support structure forming cavity, install an electrode plate system and a multi-point gating system on the mold, and configure a temperature partitioned control system and a pressure monitoring system. S3: Perform interface pretreatment. After coating the cut short glass fiber mat and continuous glass fiber mat with the interface reinforcement coating component A, place them in the corresponding outer plate forming cavity and inner plate forming cavity, with the coating surface facing inward. S4: Prepare the outer plate material, inner plate material and corrugated support structure material separately. When preparing the inner plate material, the organic modified montmorillonite is first pre-dispersed in part of the epoxy acrylate resin and then mixed with the main resin. When preparing the corrugated support structure material, prepare component A and component B separately. After vacuum degassing, each material is transferred to the reaction injection machine tank. S5: The pulsed electric field assisted reaction injection molding process is adopted. The outer plate material, corrugated support structure material and inner plate material are injected in three stages in sequence. During the second stage injection, the interface reinforcement coating component B is simultaneously coated on the surface of the corrugated support structure. When the initial viscosity of the resin reaches 0.5-1.0 Pa·s, the pulsed electric field is applied to promote interfacial bonding and fiber wetting. The injection interval of each stage is controlled within 30-90 seconds. S6: Perform simultaneous curing and post-treatment. After the three-stage injection is completed, the temperature zone control allows each layer of material to complete the main curing reaction and form an interface bond within 15-30 minutes. Finally, the mold is cooled and demolded, and the demolded composite hollow board is post-cured.

3. The preparation process according to claim 2, characterized in that, Step S1 includes: S11: Prepare component A of the interface-enhancing coating, according to the following mass ratio: 70-80 parts of epoxy resin E-44, 15-25 parts of polyurethane prepolymer, 2-3 parts of silane coupling agent KH-550, and 0.5-1.5 parts of nano-graphene. S12: When preparing component A of the interface-reinforced coating, epoxy resin E-44, polyurethane prepolymer, and silane coupling agent KH-550 are stirred at 50-70℃ for 60-90 minutes to ensure that the components are fully mixed and homogeneous. At the same time, nano-graphene is pre-dispersed in anhydrous ethanol and ultrasonically treated for 15-30 minutes. Then, the nano-graphene dispersion is added to the resin mixture and stirred for 30-60 minutes. After standing and degassing for 20-40 minutes, component A of the interface-reinforced coating is obtained. S13: Formulate component B of the interface-enhancing coating according to the following mass ratio: 60-70 parts of unsaturated polyester resin, 25-35 parts of epoxy acrylate, 2-3 parts of silane coupling agent KH-560, and 0.3-0.8 parts of functionalized carbon nanotubes. S14: When preparing component B of the interface-reinforced coating, unsaturated polyester resin, epoxy acrylate, and silane coupling agent KH-560 are stirred at 50-70℃ for 60-90 minutes to ensure that the components are fully mixed and homogeneous. At the same time, functionalized carbon nanotubes are pre-dispersed in acetone and ultrasonically treated for 15-30 minutes. Then, the carbon nanotube dispersion is added to the resin mixture and stirred for 30-60 minutes. After standing and degassing for 20-40 minutes, component B of the interface-reinforced coating is obtained.

4. The preparation process according to claim 2, characterized in that, Step S2 includes: S21: Design and process the three-cavity partition mold body, dividing the mold into three independent forming cavities. The outer plate forming cavity and the inner plate forming cavity are flat cavities, and the corrugated support structure forming cavity is designed as a corrugated curved surface. A sealing partition is set between each forming cavity to prevent different materials from penetrating each other. The mold is manufactured using CNC milling or EDM and the geometric accuracy of the curved surface is ensured. S22: Gates are provided at the crests and troughs of the corrugated support structure molding cavity, with a gate spacing of 80-120mm and a gate diameter of 3-6mm. Each gate is equipped with a needle valve nozzle controlled by a solenoid valve to open and close. 3-5 gates are evenly arranged in the outer plate molding cavity and the inner plate molding cavity, with a gate diameter of 4-8mm. A venting groove is provided at the highest point of the mold, with a venting groove depth of 0.02-0.05mm. S23: Electrode grooves are opened on the upper and lower surfaces of the mold at a distance of 5-10mm from the surface of the forming cavity. The electrode plate is embedded in the electrode groove and sealed with insulating epoxy resin. The electrode leads are led out from the side of the mold and connected to the pulse power supply. The upper surface electrode is connected to the positive terminal and the lower surface electrode is connected to the negative terminal. S24: Install heating rods and temperature sensors around each molding cavity, set different target temperatures in different areas of the corrugated support structure molding cavity to achieve temperature gradient control, install pressure sensors in each molding cavity with a range of 0-5MPa, and connect all sensors and control devices to the PLC control system.

5. The preparation process according to claim 2, characterized in that, Step S3 includes: S31: Cut the fiber reinforcement according to the size of the forming cavity. Cut the chopped glass fiber mat to the size that matches the outer plate forming cavity, and cut the continuous glass fiber mat to the size that matches the inner plate forming cavity. Check the integrity of the fiber mat to ensure that there is no damage or defects. S32: Apply the interface reinforcement coating component A to the fiber reinforcement using an ultrasonic atomization spraying device. Load the prepared interface reinforcement coating component A into the material tank of the spraying device, set the ultrasonic frequency to 1.7-2.4MHz to make the coating atomization particle size reach 5-15μm, adjust the vertical distance between the spray gun and the surface of the fiber felt to 15-25cm, and apply the coating evenly using a reciprocating spraying path. Control the coating thickness to 50-150μm, and use a thickness gauge to check the uniformity of the coating thickness. S33: Place the coated fiber felt in the molding cavity. The chopped glass fiber felt coated with component A of the interface reinforcement coating is laid flat in the outer plate molding cavity with the coated side facing inward. Ensure that the fiber felt adheres well to the cavity wall without bubbles or wrinkles. Similarly, the coated continuous glass fiber felt is laid in the inner plate molding cavity. Close the mold and apply pre-tightening force to seal the mold.

6. The preparation process according to claim 4, characterized in that, Step S4 includes: S41: Prepare the outer panel material. Add epoxy resin E-51 to a planetary mixer and stir at 60-80℃ to ensure the resin is fully mixed. Pre-wet nano-silica and silicon carbide micro powder in silane coupling agent KH-560 for 30-60 minutes and then slowly add them to the resin. Stir at high speed at 70-90℃ for 30-50 minutes to ensure the filler is fully dispersed. Add hardener 4,4-diaminodiphenylmethane and stir rapidly for 5-10 minutes. Then degas under vacuum for 15-30 minutes and adjust the viscosity to 0.3-0.8 Pa·s to obtain the outer panel reaction mixture. S42: To prepare the inner plate material, first, ultrasonically disperse the organically modified montmorillonite in epoxy acrylate for 20-40 minutes. After adding the dispersant, mix under high shear for 10-20 minutes. Then, add the vinyl ester resin, polyurethane prepolymer, carboxyl-terminated polybutadiene rubber toughening agent, and maleic anhydride-grafted polypropylene synergist in sequence. Stir and mix for 10-15 minutes after each addition. Slowly add the epoxy-amine bicore double-walled microcapsules and stir at low speed to ensure uniform dispersion, avoiding damage to the microcapsules by high-speed stirring. Add the benzoyl peroxide initiator and dimethylaniline accelerator and stir rapidly for 3-5 minutes. Degas under vacuum for 15-30 minutes and adjust the viscosity to 0.4-0.9 Pa·s to obtain the inner plate reaction mixture. S43: To prepare component A of the corrugated support structure material, stir the phthalic unsaturated polyester resin and divinylbenzene crosslinking agent at 50-70℃ for 30-50 minutes to ensure thorough mixing. Then, add the azodicarbonamide foaming agent, sodium bicarbonate and citric acid composite foaming agent, nano-calcium carbonate and talc nucleating agent, and silicone oil foaming stabilizer in sequence. Stir and mix for 10-20 minutes after each addition. Add the chopped glass fibers in batches and stir at low speed to ensure uniform fiber dispersion. Add the cyclohexanone peroxide initiator and stir rapidly for 3-5 minutes. Adjust the viscosity to 0.1-0.3 Pa·s to obtain component A of the corrugated support structure material. S44: To prepare component B of the corrugated support structure material, mix polyether polyol and castor oil-based polyol at a mass ratio of 2:1, stir at 40-60℃ for 30-50 minutes to ensure thorough mixing of the two polyols, add polycaprolactone diol shape memory enhancer and stir at 50-70℃ for 20-40 minutes to ensure full integration, add dibutyltin dilaurate catalyst and stir for 5-10 minutes, weigh the corresponding amount of 4,4-diphenylmethane diisocyanate, slowly add it to the polyol mixture and stir rapidly for 10-15 minutes to ensure thorough mixing, adjust the viscosity to 0.1-0.3 Pa·s to obtain component B of the corrugated support structure material; S45: Transfer the prepared materials to the reaction injection machine, transfer the outer plate reaction mixture to the outer plate material tank, transfer the inner plate reaction mixture to the inner plate material tank, and transfer the corrugated support structure material components A and B to their respective tanks. Set the temperature of each tank to 50-60℃ for the outer plate tank, 45-55℃ for the inner plate tank, and 40-50℃ for the corrugated support structure material tank. Turn on the circulation system to prevent material sedimentation and pre-gelling. After checking that the liquid level, temperature, and circulation pressure of each tank are normal, it is ready for use.

7. The preparation process according to claim 2, characterized in that, The S5 steps include: S51: Set the pulse electric field parameters and perform the first stage injection. In the PLC control system, set the pulse electric field parameters as follows: electric field strength 0.2-0.8kV / mm, pulse frequency 50-150Hz, duty cycle 20-40%. Start the outer plate material gate, set the injection pressure to 0.8-1.2MPa, and the mold filling speed to 300-500g / s. When the viscosity of the outer plate reaction mixture reaches 0.5-1.0Pa·s, the pulse power supply is started to apply the pulse electric field. Under the action of injection pressure and electric field, the outer plate reaction mixture enters the outer plate molding cavity and gradually impregnates the chopped glass fiber mat. When the pressure in the outer plate molding cavity reaches the set value and stabilizes, close the outer plate material gate to complete the first stage injection. S52: Perform the second stage injection. Within 30-90 seconds after the first stage injection is completed, immediately start the injection of corrugated support structure material. Pressurize component A and component B to 10-20MPa respectively through a metering pump and deliver them to the high-pressure impact mixing head at a mass ratio of 1:0.8-1.

2. The mixing head has a counter-impact structure inside, so that component A and component B are mixed at high speed and flow out immediately. Set the injection pressure to 0.5-0.9MPa. Use gate opening sequence control to open the gates from the center to both sides one by one to ensure uniform mold filling. S53: During the second stage of injection, the interface reinforcement coating component B is applied simultaneously. The interface reinforcement coating component B is sprayed onto the surface of the corrugated support structure while the corrugated support structure material is being injected using a preset coating system. The coating thickness is controlled at 30-100μm. A pulsed electric field is continuously applied to promote interfacial bonding. The second stage of injection is completed when the pressure in the curved surface forming cavity is stable. S54: Perform the third stage injection. Immediately after the second stage injection is completed, start the injection of the inner plate material. Start the inner plate material gate, set the injection pressure to 0.7-1.1MPa, and the mold filling speed to 350-550g / s. The inner plate reaction mixture enters the inner plate molding cavity under the action of injection pressure and electric field and impregnates the continuous glass fiber mat. Control the contact interface temperature between the inner plate material and the corrugated support structure material at 45-55℃ to ensure good interface bonding. When the pressure in the inner plate molding cavity is stable, close the inner plate material gate, stop the pulse electric field, and complete the third stage injection. S55: Monitors the filling status and adjusts the curing temperature. The PLC control system collects the pressure and temperature data of each molding cavity in real time, analyzes the pressure curve to determine the filling completion status of each cavity, and records the filling completion time of each layer. After the three-stage injection is completed, the PLC control system automatically switches to the curing temperature control mode, adjusts the temperature of the outer and inner plate molding cavities to 50-60℃ to promote resin curing, and maintains the temperature gradient distribution of the corrugated support structure molding cavity to achieve graded foaming.

8. The preparation process according to claim 2, characterized in that, Step S6 includes: S61: Simultaneous curing is performed to maintain the temperature stability of each molding cavity. The temperature and pressure changes in each molding cavity are monitored in real time by the PLC control system. The epoxy resin in the outer panel material undergoes a curing reaction with the hardener. The vinyl ester resin in the inner panel material undergoes free radical polymerization under the action of the initiator, while the polyurethane prepolymer forms a linear network and mixes with the main resin to form a semi-interpenetrating network structure. The unsaturated polyester resin in the corrugated support structure material crosslinks with the polyurethane elastomer to form a synchronous interpenetrating network structure. The main curing reaction of each layer is completed within 15-30 minutes by temperature zone control. The curing degree of each layer is confirmed to reach more than 85% by DSC or infrared monitoring. S62: Perform mold cooling and demolding. After curing, the PLC control system shuts down the heating system and starts the cooling system. Cooling water is circulated through the cooling water pipeline, and the cooling rate is controlled at 2-5℃ / min to avoid internal stress. When the mold temperature drops to 40-45℃ and remains stable for more than 10 minutes, the PLC control system sends a demolding signal and starts the hydraulic system to open the mold. The mold opening speed is 10-30mm / min. Use demolding tools to gently remove the composite hollow board from the mold. S63: Perform post-curing treatment. Place the demolded composite hollow board in a special post-curing oven. Set the oven temperature to 80-120℃ and the heating rate to 2-5℃ / min. After the oven temperature reaches the set temperature, keep it at that temperature for 2-4 hours to perform post-curing treatment to eliminate internal stress and improve the degree of curing. After the post-curing treatment is completed, turn off the oven heating system and let it cool naturally to below 60℃. Open the oven door to allow the product to continue cooling to room temperature inside the oven. The cooling rate should not exceed 3℃ / min.

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