Aluminum-plastic panel and composite processing technology thereof

Abstract

This invention discloses an aluminum composite panel and its composite processing technology, belonging to the technical field of building decoration materials. The aluminum composite panel includes an aluminum alloy panel, a core layer, and an in-situ anchored gradient interface bonding layer and a bifunctional grafted polyolefin hot melt adhesive film layer sequentially disposed between the two. A porous micro-arc oxidation ceramic substrate film is generated in-situ on the inner surface of the aluminum alloy panel. The gradient interface bonding layer is a silane coupling agent-epoxy functional group grafted modified layer, anchored and filled within the pores to form a continuous transition film. The core layer contains a synergistic halogen-free flame retardant of hydroxylated basalt fibers and needle-like wollastonite fibers. The composite process uses low-temperature reactive hot pressing at 130-160℃ to induce ring-opening chemical bonding of the interface epoxy groups. The aluminum composite panel of this invention has a peel strength ≥160N / 25mm, a retention rate ≥90% after thermal cycling, a flame retardancy rating of V-0, and an impact strength ≥15kJ / m². 2 It combines excellent interface bonding, flame retardant toughness, and environmental protection characteristics.

Description

Technical Field

[0001] This invention relates to the field of building decoration materials technology, and in particular to an aluminum composite panel and its composite processing technology. Background Technology

[0002] Aluminum composite panels, or ACPs for short, are widely used in building curtain walls, interior decoration, and transportation due to their advantages such as lightweight, high strength, good flatness, and rich colors. A typical ACP structure consists of a five-layer sandwich structure: aluminum alloy panel, polymer film, polyethylene core layer, polymer film, and aluminum alloy panel. However, with the upgrading of building fire protection standards and the increasing safety requirements for high-rise curtain walls, traditional ACPs face the following technical challenges; Aluminum alloys are high-surface-energy inorganic materials, while the polyethylene core layer is a low-surface-energy organic polymer material; their physicochemical properties differ significantly. Currently, industrially, chromate passivation is commonly used to increase the roughness of aluminum plates, followed by hot-pressing bonding using a monofunctional hot-melt adhesive film (such as maleic anhydride-grafted polyethylene). This interfacial bonding relies primarily on physical adsorption and weak hydrogen bonds, lacking strong chemical bonds. After prolonged exposure to ultraviolet radiation, humidity, and extreme temperature cycles ranging from -40°C to 80°C outdoors, the thermal stress generated by the difference in thermal expansion coefficients between the aluminum plate and the core layer continuously damages the physical bonding interface, leading to a significant decrease in peel strength and even serious quality issues such as blistering, delamination, and separation. Furthermore, the hexavalent chromium passivation process poses serious hazards to the environment and human health.

[0003] Currently, it is mandatory for aluminum composite panels used in the curtain walls of high-rise buildings to meet B1 (fire-retardant) or even higher standards. To meet halogen-free environmental protection requirements, the industry typically adds large amounts of inorganic flame-retardant fillers such as aluminum hydroxide (ATH) or magnesium hydroxide (MH) to the polyethylene core layer, with the filler content needing to be as high as 50wt%-65wt% to pass the B1 flammability test. However, the high filler content of inorganic powders severely damages the continuity of the polyethylene matrix, leading to a sharp increase in the brittleness of the core layer, and the impact strength of simply supported beams is generally lower than 8kJ / m. 2 During bending processing, it is very easy to crack at the corner, which greatly limits the application of aluminum composite panels in irregular shapes.

[0004] Ordinary inorganic flame retardants function only by decomposing and absorbing heat and diluting combustible gases during polyethylene combustion, and cannot form a self-supporting, robust char layer. Molten polyethylene dripping carries away heat and disrupts the continuity of the char layer, leading to flame retardant failure. Current technologies lack effective means to synergistically strengthen the char layer skeleton and suppress dripping during combustion.

[0005] Traditional hot-pressing lamination of aluminum composite panels typically involves temperatures as high as 180℃-200℃, aiming to ensure the hot melt adhesive fully melts and flows smoothly. However, high temperatures can cause the aluminum alloy panel to soften during annealing, the surface coating to age and discolor, and the core layer flame retardant to decompose prematurely at high temperatures, generating moisture and forming bubble defects at the interface. Furthermore, high temperatures only promote physical fusion and cannot induce chemical bonding reactions, thus the interfacial bonding potential remains largely untapped. Summary of the Invention

[0006] The purpose of this invention is to provide an aluminum composite panel and its composite processing technology to solve the above-mentioned problems.

[0007] This invention provides an aluminum composite panel, comprising an upper aluminum alloy panel layer, an intermediate core layer, and a lower aluminum alloy panel layer stacked sequentially. An in-situ anchored gradient interface bonding layer and a bifunctional grafted polyolefin hot melt adhesive film layer are sequentially provided between the upper aluminum alloy panel layer and the middle core layer, and between the lower aluminum alloy panel layer and the middle core layer. On the inner surfaces of the upper aluminum alloy panel layer and the lower aluminum alloy panel layer facing the middle core layer, a porous micro-arc oxidation ceramic substrate film is generated in situ. The in-situ anchored gradient interface bonding layer is a silane coupling agent-epoxy functional group grafted modification layer, and the modification layer is anchored and filled in the pores of the porous micro-arc oxidation ceramic substrate film and forms a continuous transition film on the film surface. The bifunctional grafted polyolefin hot melt adhesive film layer is a maleic anhydride-epoxy double-grafted linear low-density polyethylene hot melt adhesive film layer. The intermediate core layer is a halogen-free flame-retardant reinforced polyethylene composite core layer with synergistic effects of hydroxylated basalt fibers and acicular wollastonite fibers.

[0008] Preferably, both the upper and lower aluminum alloy panel layers are made of 3003 or 3004 series rust-proof aluminum alloy sheets with a thickness of 0.15 to 0.50 mm; the porous micro-arc oxidation ceramic substrate film has a thickness of 2 to 10 μm, a surface porosity of 15% to 30%, and an average pore size of 50 to 200 nm.

[0009] Preferably, the total thickness of the in-situ anchored gradient interface bonding layer is 1–4 μm, wherein the anchored portion within the pores accounts for no less than 40%; the in-situ anchored gradient interface bonding layer is formed by grafting a silane coupling agent and an epoxy resin oligomer, wherein the mass ratio of the silane coupling agent to the epoxy resin oligomer is 1:0.3–1:0.8; wherein the silane coupling agent is one of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane, and the epoxy resin oligomer is a bisphenol A type epoxy resin oligomer.

[0010] Preferably, the thickness of the bifunctional grafted polyolefin hot melt adhesive film layer is 20-60 μm, and its raw material composition by weight is: 50-70 parts of maleic anhydride-epoxy double-grafted linear low-density polyethylene, 8-18 parts of tackifying resin, 1-6 parts of epoxy silane modified nano-fumed silica, and 0.5-1.5 parts of crosslinking agent; the maleic anhydride grafting rate of the double-grafted linear low-density polyethylene is 0.8%-1.5%, and the epoxy grafting rate is 0.5%-1.2%.

[0011] Preferably, the thickness of the intermediate core layer is 2-5 mm, and its raw material composition by weight is: 35-55 parts high-density polyethylene, 10-25 parts linear low-density polyethylene, 22-38 parts nitrogen-phosphorus intumescent flame retardant, 4-12 parts hydroxylated modified basalt fiber chopped strands, 3-8 parts needle-shaped wollastonite fiber, 2-7 parts maleic anhydride-grafted polyethylene compatibilizer, and 0.2-0.8 parts antioxidant; the surface hydroxyl content of the hydroxylated modified basalt fiber chopped strands is ≥0.8 mmol / g, and the length is 2-5 mm; the average length of the needle-shaped wollastonite fiber is 20-80 μm, and the aspect ratio is 8:1-15:1.

[0012] Preferably, the outer surface of the upper aluminum alloy panel layer is provided with a weather-resistant fluorocarbon coating or a polyester coating, with a coating thickness of 15 to 40 μm; the outer surface of the lower aluminum alloy panel layer is provided with an anti-corrosion polyester coating, with a thickness of 8 to 25 μm.

[0013] A composite processing technology for aluminum composite panels as described above is provided, comprising the following steps: S1. Micro-arc oxidation treatment is performed on the surfaces of the upper and lower aluminum alloy panel layers to be composited to generate a porous ceramic substrate film with a thickness of 2-10 μm, a surface porosity of 15%-30%, and an average pore size of 50-200 nm in situ. S2. The panel after micro-arc oxidation treatment is immersed in a mixed modification liquid containing silane coupling agent and epoxy functional group monomer. Under vacuum negative pressure, the modification liquid is allowed to penetrate and fill the pores of the porous ceramic substrate film. After removal, it is dried and cured by gradient hot air at 80-120°C to form the in-situ anchored gradient interface bonding layer on the panel surface. S3. Prepare the intermediate core layer by weighing 35-55 parts of high-density polyethylene, 10-25 parts of linear low-density polyethylene, 22-38 parts of nitrogen-phosphorus intumescent flame retardant, 4-12 parts of hydroxylated modified basalt fiber chopped strands, 3-8 parts of needle-like wollastonite fiber, 2-7 parts of maleic anhydride grafted polyethylene compatibilizer, and 0.2-0.8 parts of antioxidant. After melt blending and granulation in a twin-screw extruder, the intermediate core layer is formed by sheet extrusion. The twin-screw extrusion temperature is: 150-170℃ in the feeding section, 170-190℃ in the compression section, and 180-200℃ in the metering section. S4. Prepare a bifunctional grafted polyolefin hot melt adhesive film by weighing 50-70 parts of maleic anhydride-epoxy double-grafted linear low-density polyethylene, 8-18 parts of tackifying resin, 1-6 parts of epoxy silane modified nano-fumed silica, and 0.5-1.5 parts of crosslinking agent, and then casting the film to obtain the bifunctional grafted polyolefin hot melt adhesive film. S5. The upper aluminum alloy panel layer, the first bifunctional grafted polyolefin hot melt adhesive film layer, the intermediate core layer, the second bifunctional grafted polyolefin hot melt adhesive film layer, and the lower aluminum alloy panel layer are stacked in sequence and fed into a continuous hot pressing composite equipment. Hot pressing composite is carried out at a temperature of 130-160℃ and a pressure of 0.5-2.0MPa. During the composite process, the epoxy groups of the hot melt adhesive film layer and the epoxy functional groups of the gradient interface bonding layer undergo a ring-opening chemical bonding reaction. S6. The composite board is gradually cooled to below 40°C under pressure, and then trimmed and cut to obtain the finished aluminum composite panel.

[0014] Preferably, in step S1, before the micro-arc oxidation treatment, the surface of the aluminum alloy panel is first subjected to low-temperature plasma activation pretreatment. The treatment parameters are: a mixed gas atmosphere with an argon to oxygen volume ratio of 4:1 to 9:1, a treatment power of 200 to 400W, and a treatment time of 60 to 120s.

[0015] Preferably, the total mass concentration of the mixed modified liquid in step S2 is 2% to 6%, and the solvent is a mixed solvent of ethanol and water in a volume ratio of 8:2 to 9:1; the absolute pressure of the vacuum negative pressure condition is 10 to 50 kPa, and the immersion time is 10 to 30 min.

[0016] Preferably, the continuous hot pressing composite in step S5 adopts a continuous hot pressing roller composite method, with a hot pressing roller linear pressure of 15-50 N / mm and a feeding speed of 2-8 m / min; and the laminated boards are pre-pressed before hot pressing composite, with a pre-pressing temperature of 80-100℃, a pre-pressing pressure of 0.2-0.5 MPa, and a pre-pressing time of 5-10 min.

[0017] Therefore, the present invention, employing the above-mentioned aluminum composite panel and its composite processing technology, has the following beneficial effects: (1) A porous ceramic film of 50-200 nm is generated in situ on the surface of aluminum alloy by micro-arc oxidation, and then a silane-epoxy gradient interface bonding layer with a pore anchoring ratio of ≥40% is formed by vacuum negative pressure impregnation. During hot pressing, the epoxy functional groups of this interface layer undergo ring-opening chemical bonding with the epoxy groups of the bifunctional hot melt adhesive film, forming a dual anchoring system of "mechanical interlocking and chemical cross-linking of ceramic film". The resulting aluminum composite panel has a peel strength of ≥160 N / 25 mm, and the strength retention rate is ≥90% after 100 cycles of hot and cold cycling from -40℃ to 80℃, which far exceeds the national standard requirements.

[0018] (2) The core layer adopts a synergistic system of hydroxylated basalt fiber and acicular wollastonite fiber. During combustion, the hydroxylated fiber undergoes an esterification reaction with the pyrolysis products of the flame retardant to form a dense ceramicized carbon layer with fiber as the skeleton, effectively suppressing dripping; the acicular wollastonite fiber constrains the thermal expansion of polyethylene and reduces interfacial stress. When the amount of flame retardant added is only 22-38 parts, the limiting oxygen index is ≥34%, the vertical combustion reaches V-0 level, and the simply supported beam impact strength is ≥15kJ / m. 2 With a bending strength ≥80MPa, it achieves a balance between flame retardancy and mechanical properties.

[0019] (3) The hot pressing temperature of the composite process is controlled at 130-160℃, precisely matching the activation energy of the ring-opening reaction of epoxy groups, so that the interfacial chemical bonding and hot pressing are completed simultaneously. This avoids the problems of aluminum plate deformation and coating aging caused by traditional high-temperature composites. Combined with the gradient cooling process, the interlayer internal stress is effectively eliminated, and the flatness deviation of the plate section is ≤0.05mm / m.

[0020] (4) The fully green interface treatment process of micro-arc oxidation and silane coupling grafting is adopted to replace the traditional chromate passivation, which meets environmental protection requirements. The fluorocarbon or polyester coating on the outer surface provides excellent weather protection and extends the service life of the product.

[0021] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0022] To better understand the above technical solutions, a detailed description of the specific implementation methods will be provided below. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0024] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0025] Example 1 (1) Pretreatment of aluminum alloy panels and construction of interface layer; A 0.30mm thick 3003 series aluminum alloy sheet was used as the upper and lower aluminum alloy panel layers. First, the surface of the panel to be laminated underwent low-temperature plasma activation pretreatment: a mixture of argon and oxygen in a 6:1 volume ratio was introduced into a dielectric barrier discharge device, with a treatment power of 300W and a treatment time of 90s, reducing the surface water contact angle to 28°. Subsequently, the panel was placed in a micro-arc oxidation electrolyte and treated in a constant current mode for 15 minutes, resulting in the in-situ formation of a porous ceramic substrate film with a thickness of approximately 6μm, a porosity of 22%, and an average pore size of 120nm.

[0026] The panel treated with micro-arc oxidation was immersed in a vacuum impregnation tank and injected with a mixed modification solution. The modification solution formulation was as follows: γ-glycidyl etheroxypropyltrimethoxysilane (KH560) and bisphenol A type epoxy resin oligomer (E-44) were dissolved in a mixed solvent of ethanol and water at a mass ratio of 1:0.5 and a volume ratio of 9:1, with a total mass concentration of 4%. The panel was impregnated under a negative pressure of 30 kPa for 20 minutes to allow the modification solution to fully penetrate into the pores. After removal, the panel was pre-baked at 60°C for 10 minutes, then gradually heated to 100°C and cured for 20 minutes to form an in-situ anchored gradient interface bonding layer with a total thickness of approximately 2.5 μm, with the anchored portion accounting for approximately 48% of the pores.

[0027] (2) Preparation of bifunctional hot melt adhesive film; By weight: 60 parts of maleic anhydride-epoxy double-grafted linear low-density polyethylene (MAH grafting rate 1.1%, epoxy grafting rate 0.8%, MFR=10g / 10min), 12 parts of C5 petroleum resin tackifier, 4 parts of epoxy silane (KH560) modified nano-fumed silica (average particle size 20nm), 1.0 part of dicumyl peroxide (DCP), and 0.2 parts of antioxidant 1010 were mixed evenly in a high-speed mixer, melt-granulated at 160-180℃ using a twin-screw extruder, and then cast into a film at a die temperature of 170℃ using a single-layer casting machine to obtain a 40μm thick bifunctional grafted polyolefin hot melt adhesive film.

[0028] (3) Preparation of synergistic flame-retardant reinforced core layer; By weight: 45 parts high-density polyethylene (HDPE, MFR=0.5g / 10min), 18 parts linear low-density polyethylene (LLDPE, MFR=2g / 10min), 30 parts nitrogen-phosphorus intumescent flame retardant, 8 parts hydroxylated modified basalt fiber chopped strands, 5 parts needle-like wollastonite fiber, 5 parts maleic anhydride grafted polyethylene compatibilizer (MAH-g-PE, grafting rate 1.0%), 0.5 parts antioxidant 1010 / 168 compound, and 0.8 parts zinc stearate. Nitrogen-phosphorus intumescent flame retardants include ammonium polyphosphate, dipentaerythritol, and melamine cyanurate, with a polyphosphate:dipentaerythritol:melamine cyanurate ratio of 4:1:1.5; the hydroxylated modified basalt fiber chopped strands have a length of 3 mm, a single filament diameter of 10 μm, and a surface hydroxyl content of 1.1 mmol / g; the needle-like wollastonite fibers have an average length of 45 μm and an aspect ratio of 12:1; The above raw materials are mixed evenly in a high-speed mixer, and then melt-blended and granulated by a twin-screw extruder. The extrusion temperature is 160°C in the feeding section, 180°C in the compression section, and 190°C in the metering section. The granules are then extruded into sheets by a single-screw extruder with a die temperature of 190°C to obtain a core layer board with a thickness of 3.0 mm.

[0029] (4) Low-temperature reaction recombination; The aluminum alloy panel is simultaneously unwound and stacked in the following order: upper aluminum alloy panel / first hot-melt adhesive film grafted with bifunctional groups of polyolefin / core layer board / second hot-melt adhesive film grafted with bifunctional groups of polyolefin / lower aluminum alloy panel. Pre-pressing is performed first through a preheating section and pre-pressing rollers. The preheating section temperature is 100℃, and the pre-pressing roller pressure is 0.3MPa. Then, the panel enters the double-roll hot-pressing section. The hot-pressing roller temperature is 150℃, the linear pressure is 30N / mm, and the feed speed is 4m / min. During the hot-pressing process, the epoxy groups in the hot-melt adhesive film undergo a ring-opening cross-linking reaction with the epoxy functional groups on the surface of the gradient interface bonding layer. After lamination, the board is shaped under a gradient cooling section at 0.5MPa holding pressure; it is first passed through a 100℃ heat-insulating roller, then through a 60℃ air-cooling system, and finally cooled to room temperature.

[0030] (5) Post-processing; After cooling, the sheet material is trimmed, coated with a protective film, and cut to length to obtain a finished aluminum composite panel with a total thickness of 3.5mm. The outer surface of the upper aluminum alloy panel is pre-coated with a 25μm fluorocarbon coating (PVDF), and the outer surface of the lower aluminum alloy panel is coated with a 15μm polyester coating.

[0031] Example 2 The difference from Example 1 is that in step (3) of the core layer formulation, the hydroxylated modified basalt fiber chopped yarn is adjusted to 12 parts and the needle-like wollastonite fiber is adjusted to 3 parts; the silane coupling agent in the mixed modification liquid in step (1) is replaced with γ-aminopropyltriethoxysilane (KH550). The remaining processes and parameters are the same as in Example 1.

[0032] Example 3 The difference from Example 1 is as follows: In step (3), the nitrogen-phosphorus intumescent flame retardant in the core layer formulation is adjusted to 38 parts, the hydroxylated modified basalt fiber is adjusted to 5 parts, and the needle-like wollastonite fiber is adjusted to 8 parts; in step (2), the maleic anhydride-epoxy double-grafted LLDPE in the hot melt adhesive film is adjusted to 70 parts, and the nano-fumed silica is adjusted to 6 parts; in step (5), the hot pressing temperature is adjusted to 140℃ and the pressure to 1.5MPa. The rest is the same as in Example 1.

[0033] Example 4 The difference from Example 1 is that in step (1), the low-temperature plasma activation pretreatment is not performed, and the micro-arc oxidation treatment is performed directly. The rest is the same as in Example 1.

[0034] Comparative Example 1 The aluminum alloy panel undergoes conventional chromate passivation treatment, with a chromate film thickness of approximately 0.5 μm. The hot melt adhesive film is made of ordinary maleic anhydride-grafted polyethylene (MAH-g-PE, grafting rate 0.9%), free of epoxy functional groups, with a thickness of 40 μm. The core layer, by weight, consists of: 40 parts HDPE, 15 parts LLDPE, 60 parts aluminum hydroxide (ATH), 4 parts MAH-g-PE, and 0.5 parts antioxidant, extruded via twin-screw extrusion, with a thickness of 3.0 mm. The composite process involves hot pressing at 180°C and 1.5 MPa for 15 minutes using a conventional hot press, followed by natural cooling. Other aspects are the same as in Example 1.

[0035] Comparative Example 2 The aluminum alloy panel undergoes micro-arc oxidation treatment, as in Example 1; and is impregnated with a pure silane coupling agent solution, KH560 only, without epoxy resin oligomers. The hot melt adhesive film is ordinary MAH-g-PE, as in Comparative Example 1. The core layer and composite process are the same as in Example 1.

[0036] Comparative Example 3 The difference from Example 1 is that hydroxylated basalt fiber and needle-like wollastonite fiber are not added to the core layer formulation in step (3), and the nitrogen-phosphorus intumescent flame retardant is adjusted to 45 parts. The rest is the same as in Example 1.

[0037] Comparative Example 4 The difference from Example 1 is that the composite process in step (5) uses a traditional flatbed hot press with a hot pressing temperature of 185°C, a pressure of 1.5 MPa, a hot pressing time of 15 min, and no gradient cooling. The rest is the same as in Example 1.

[0038] The performance of the aluminum composite panels prepared in each embodiment and comparative example was tested. The test standards and results are shown in Table 1 below. Table 1 Performance Test Results

[0039] The test results above show that: The initial peel strength of Examples 1-4 was ≥165 N / 25 mm, significantly higher than that of Comparative Example 1 (72 N / 25 mm) and Comparative Example 2 (98 N / 25 mm). Especially after 100 rigorous thermal cycles, the peel strength retention rate of Examples 1-4 was above 89%, while that of Comparative Example 1 decreased sharply to 38 N / 25 mm (52.8%), and that of Comparative Example 2 dropped to 62 N / 25 mm (63.3%). The synergistic interface system of micro-arc oxidation porous ceramic membrane anchoring, silane-epoxy gradient interface layer, and bifunctional hot melt adhesive chemical bonding in this invention can form a strong and thermally fatigue-resistant chemical bonding interface, solving the problem of easy delamination in traditional aluminum composite panels. Example 4, due to the omission of plasma activation pretreatment, showed a slight decrease in initial interface bonding strength, but it was still far superior to the comparative examples.

[0040] Examples 1-4 all exhibited limiting oxygen indices ≥36%, achieved V-0 rating during vertical combustion, and had simply supported beam impact strength ≥16.8 kJ / m². 2 This achieves a perfect balance between high flame retardancy and high toughness. Comparative Example 1, using traditional ATH filler, has a LOI of only 27% and an impact strength of only 7.5 kJ / m². 2 Both flame retardancy and mechanical properties were poor. Comparative Example 3, without added fiber, despite increasing the flame retardant to 45 parts, still had an LOI of only 31% and a V-1 rating, with impact strength reduced to 12.3 kJ / m². 2 This indicates that simply adding flame retardants cannot effectively improve flame retardant efficiency; on the contrary, it severely degrades mechanical properties. This invention achieves a V-0 rating with only about 30 parts of flame retardant added, through the synergistic effect of esterification of hydroxylated basalt fibers and flame retardants, and the reinforcement of acicular wollastonite fibers, while also exhibiting excellent mechanical properties.

[0041] Comparative Example 4 used traditional high-temperature (185℃) lamination. Due to the high temperature, the aluminum plate underwent slight annealing deformation and the core layer flame retardant decomposed slightly, increasing the flatness deviation of the plate cross-section to 0.09mm / m and reducing the surface coating adhesion to level 2. In contrast, this invention uses low-temperature reaction lamination at 130-160℃ combined with gradient cooling, which ensures the full progress of the interfacial chemical reaction while avoiding thermal damage, significantly improving the product's dimensional accuracy and appearance quality.

[0042] Therefore, this invention employs the aforementioned aluminum composite panel and its composite processing technology, using micro-arc oxidation technology to generate a porous ceramic substrate film in situ on the inner surface of the aluminum alloy panel. Its unique three-dimensional interconnected channels provide a strong "root anchoring" physical basis for interface bonding. Through a vacuum negative pressure impregnation process, a silane coupling agent-epoxy functional group grafted modified layer is penetrated and cured deep within the channels, forming an in-situ anchored gradient interface bonding layer with an in-situ anchoring ratio of not less than 40%. During the hot-pressing composite stage, the epoxy functional groups on the surface of this gradient interface layer undergo a ring-opening crosslinking reaction with the epoxy groups in the bifunctional grafted polyolefin hot melt adhesive film, constructing a five-level continuous chemical bonding network: aluminum alloy substrate—ceramic film (mechanical interlocking)—silane-epoxy bridging layer (chemical bonding)—hot melt adhesive film (molecular compatibility)—core layer. This structure enables a breakthrough in interlayer peel strength under normal conditions, reaching ≥160N / 25mm, far exceeding the 60N / 25mm requirement of the national standard GB / T 17748-2016. After 100 cycles of high and low temperatures from -40℃ to 80℃, the peel strength retention rate is still over 90%, completely solving the potential delamination problem during long-term outdoor use.

[0043] The intermediate core layer employs a "two-phase fiber synergy" system, combining hydroxylated basalt fibers and acicular wollastonite fibers. The hydroxylated basalt fibers, rich in hydroxyl groups (≥0.8 mmol / g), undergo in-situ esterification with phosphoric acid / polyphosphoric acid produced by the decomposition of nitrogen-phosphorus intumescent flame retardants at high combustion temperatures, forming a ceramicized barrier layer with high-melting-point basalt fibers as the framework and a dense cross-linked carbon layer as the filler. This structure effectively suppresses the dripping of polyethylene melt and significantly improves the strength and thermal insulation performance of the carbon layer. The acicular wollastonite fibers form a dispersed reinforcing network within the core matrix, exhibiting an extremely low coefficient of thermal expansion (approximately 6.5 × 10⁻⁶). -6 The flame retardant effectively constrains the thermal expansion and contraction deformation of polyethylene, reducing the interfacial thermal stress between the core layer and the aluminum plate. With only 22-38 parts of flame retardant added, the core layer's limiting oxygen index is ≥34%, achieving V-0 rating in vertical combustion; simultaneously, the simply supported beam impact strength is ≥15kJ / m². 2 With a bending strength ≥80MPa, it achieves a 1.5-2 times increase in toughness and can be perfectly adapted to complex processing techniques such as grooving and bending.

[0044] The composite processing technology precisely controls the hot-pressing temperature between 130-160℃. This temperature window ensures sufficient activation and flow of the hot melt adhesive film while remaining below the thermal decomposition temperature of polyethylene and the flame retardant, preventing core layer foaming and thermal softening deformation of the aluminum plate. Simultaneously, this temperature precisely matches the ring-opening reaction activation energy of the epoxy groups, enabling simultaneous completion of hot-pressing and interfacial chemical cross-linking, eliminating the need for additional post-curing treatment. Combined with a gradient cooling and shaping process, interlayer stress is effectively eliminated, resulting in a sheet cross-sectional flatness deviation of ≤0.05mm / m.

[0045] This process abandons traditional dichromate passivation and adopts a fully green interface construction technology combining micro-arc oxidation and silane treatment, complying with international environmental directives such as RoHS. Combined with a weather-resistant fluorocarbon coating on the outer surface, it gives the aluminum composite panel excellent resistance to ultraviolet rays and acid and alkali corrosion, significantly extending its service life.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An aluminum composite panel, comprising an upper aluminum alloy panel layer, an intermediate core layer, and a lower aluminum alloy panel layer stacked sequentially, characterized in that: An in-situ anchored gradient interface bonding layer and a bifunctional grafted polyolefin hot melt adhesive film layer are sequentially provided between the upper aluminum alloy panel layer and the middle core layer, and between the lower aluminum alloy panel layer and the middle core layer. On the inner surfaces of the upper aluminum alloy panel layer and the lower aluminum alloy panel layer facing the middle core layer, a porous micro-arc oxidation ceramic substrate film is generated in situ. The in-situ anchored gradient interface bonding layer is a silane coupling agent-epoxy functional group grafted modification layer, and the modification layer is anchored and filled in the pores of the porous micro-arc oxidation ceramic substrate film and forms a continuous transition film on the film surface. The bifunctional grafted polyolefin hot melt adhesive film layer is a maleic anhydride-epoxy double-grafted linear low-density polyethylene hot melt adhesive film layer. The intermediate core layer is a halogen-free flame-retardant reinforced polyethylene composite core layer with synergistic effects of hydroxylated basalt fibers and acicular wollastonite fibers.

2. The aluminum composite panel according to claim 1, characterized in that, The thickness of the upper and lower aluminum alloy panel layers is 0.15–0.50 mm; the thickness of the porous micro-arc oxidation ceramic substrate film is 2–10 μm, the surface porosity is 15%–30%, and the average pore size is 50–200 nm.

3. The aluminum composite panel according to claim 1, characterized in that, The total thickness of the in-situ anchored gradient interface bonding layer is 1–4 μm, wherein the anchored portion within the pores accounts for no less than 40%; the in-situ anchored gradient interface bonding layer is formed by grafting a silane coupling agent and an epoxy resin oligomer, wherein the mass ratio of the silane coupling agent to the epoxy resin oligomer is 1:0.3–1:0.8; wherein the silane coupling agent is one of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane, and the epoxy resin oligomer is a bisphenol A type epoxy resin oligomer.

4. An aluminum composite panel according to claim 1, characterized in that, The thickness of the bifunctional grafted polyolefin hot melt adhesive film layer is 20-60 μm. By weight, its raw material composition is: 50-70 parts of maleic anhydride-epoxy double-grafted linear low-density polyethylene, 8-18 parts of tackifying resin, 1-6 parts of epoxy silane modified nano-fumed silica, and 0.5-1.5 parts of crosslinking agent; the maleic anhydride grafting rate of the double-grafted linear low-density polyethylene is 0.8%-1.5%, and the epoxy grafting rate is 0.5%-1.2%.

5. An aluminum composite panel according to claim 1, characterized in that, The thickness of the intermediate core layer is 2-5 mm, and its raw material composition by weight is: 35-55 parts high-density polyethylene, 10-25 parts linear low-density polyethylene, 22-38 parts nitrogen-phosphorus intumescent flame retardant, 4-12 parts hydroxylated modified basalt fiber chopped strands, 3-8 parts needle-shaped wollastonite fiber, 2-7 parts maleic anhydride grafted polyethylene compatibilizer, and 0.2-0.8 parts antioxidant; the surface hydroxyl content of the hydroxylated modified basalt fiber chopped strands is ≥0.8 mmol / g, and the length is 2-5 mm; the average length of the needle-shaped wollastonite fiber is 20-80 μm, and the aspect ratio is 8:1-15:

1.

6. An aluminum composite panel according to claim 1, characterized in that, The outer surface of the upper aluminum alloy panel layer is provided with a weather-resistant fluorocarbon coating or a polyester coating with a coating thickness of 15 to 40 μm; the outer surface of the lower aluminum alloy panel layer is provided with an anti-corrosion polyester coating with a thickness of 8 to 25 μm.

7. A composite processing technology for aluminum composite panels as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Micro-arc oxidation treatment is performed on the surfaces of the upper and lower aluminum alloy panel layers to be composited to generate a porous ceramic substrate film with a thickness of 2-10 μm, a surface porosity of 15%-30%, and an average pore size of 50-200 nm in situ. S2. The panel after micro-arc oxidation treatment is immersed in a mixed modification liquid containing silane coupling agent and epoxy functional group monomer. Under vacuum negative pressure, the modification liquid is allowed to penetrate and fill the pores of the porous ceramic substrate film. After removal, it is dried and cured by gradient hot air at 80-120°C to form the in-situ anchored gradient interface bonding layer on the panel surface. S3. Prepare the intermediate core layer by weighing 35-55 parts of high-density polyethylene, 10-25 parts of linear low-density polyethylene, 22-38 parts of nitrogen-phosphorus intumescent flame retardant, 4-12 parts of hydroxylated modified basalt fiber chopped strands, 3-8 parts of needle-like wollastonite fiber, 2-7 parts of maleic anhydride grafted polyethylene compatibilizer, and 0.2-0.8 parts of antioxidant. After melt blending and granulation in a twin-screw extruder, the intermediate core layer is formed by sheet extrusion. The twin-screw extrusion temperature is: 150-170℃ in the feeding section, 170-190℃ in the compression section, and 180-200℃ in the metering section. S4. Prepare a bifunctional grafted polyolefin hot melt adhesive film by weighing 50-70 parts of maleic anhydride-epoxy double-grafted linear low-density polyethylene, 8-18 parts of tackifying resin, 1-6 parts of epoxy silane modified nano-fumed silica, and 0.5-1.5 parts of crosslinking agent, and then casting the film to obtain the bifunctional grafted polyolefin hot melt adhesive film. S5. The upper aluminum alloy panel layer, the first bifunctional grafted polyolefin hot melt adhesive film layer, the intermediate core layer, the second bifunctional grafted polyolefin hot melt adhesive film layer, and the lower aluminum alloy panel layer are stacked in sequence and fed into a continuous hot pressing composite equipment. Hot pressing composite is carried out at a temperature of 130-160℃ and a pressure of 0.5-2.0MPa. During the composite process, the epoxy groups of the hot melt adhesive film layer and the epoxy functional groups of the gradient interface bonding layer undergo a ring-opening chemical bonding reaction. S6. The composite board is gradually cooled to below 40°C under pressure, and then trimmed and cut to obtain the finished aluminum composite panel.

8. The aluminum composite panel composite processing technology according to claim 7, characterized in that, In step S1, before the micro-arc oxidation treatment, the surface of the aluminum alloy panel is first subjected to low-temperature plasma activation pretreatment. The treatment parameters are: a mixed gas atmosphere with an argon to oxygen volume ratio of 4:1 to 9:1, a treatment power of 200 to 400W, and a treatment time of 60 to 120s.

9. The aluminum composite panel composite processing technology according to claim 7, characterized in that, The total mass concentration of the mixed modified liquid in step S2 is 2% to 6%, and the solvent is a mixed solvent of ethanol and water with a volume ratio of 8:2 to 9:1; the absolute pressure of the vacuum negative pressure condition is 10 to 50 kPa, and the immersion time is 10 to 30 min.

10. The aluminum composite panel processing technology according to claim 7, characterized in that, The continuous hot-pressing composite method described in step S5 adopts a continuous hot-pressing roller composite method. The hot-pressing roller linear pressure is 15-50 N / mm and the material feeding speed is 2-8 m / min. Before hot-pressing composite, the laminated boards are pre-pressed. The pre-pressing temperature is 80-100℃, the pre-pressing pressure is 0.2-0.5 MPa, and the pre-pressing time is 5-10 min.

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