Aluminum-plastic composite panel for indoor decoration and preparation method of aluminum-plastic composite panel

Abstract

The invention provides an aluminum-plastic composite panel for indoor decoration and a preparation method, and belongs to the technical field of composite panel preparation. The aluminum-plastic composite plate comprises a chromium-free passivated back aluminum alloy plate, a lower adhesive film, an LDPE flame-retardant core layer, an upper adhesive film and a chromium-free blunt-surface aluminum alloy plate, wherein a flexible epoxy interface bonding transition layer, a pattern decoration layer and a PVDF protection layer are sequentially arranged on the upper surface of the chromium-free blunt-surface aluminum alloy plate. The preparation method comprises the steps of chromium-free passivation, primer coating, preparation of the functional coating, preparation of the flame-retardant core layer, preparation of the composite adhesive film, pre-lamination and hot-press compounding. Through matched material system design and an innovative manufacturing process, a solution with excellent comprehensive performance is provided for production of the aluminum-plastic composite panel in the aspects of environmental protection, flame retardance, interface bonding reliability and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of composite board preparation, and relates to an aluminum-plastic composite board for interior decoration and a preparation method thereof. Background Art

[0002] Aluminum-plastic composite panels (APCs) are widely used in interior decoration due to their lightweight, easy processing, and decorative properties. However, existing products and their manufacturing processes still face significant challenges. Regarding environmental performance, hexavalent chromium pollution from the chromate passivation process is a significant concern, necessitating the development of environmentally friendly, chromium-free passivation alternatives. Regarding core performance, highly filled flame-retardant core layers often suffer from uneven flame retardant dispersion, easy migration and precipitation, significantly degraded mechanical properties, and weakened interfacial bonding with traditional adhesive films, leading to a risk of flame retardant continuity failure. Addressing the technical bottleneck of flame retardancy-mechanical-interface synergistic reinforcement is crucial. Regarding structural reliability, the lack of a flexible stress buffer between the aluminum sheet and the decorative layer can easily lead to delamination of the decorative layer, resulting in weak impact protection for the backsheet, and warping and deformation caused by the high flame-retardant fillers during core layer processing. Systematic optimization of the interlayer structure and processing techniques is urgently needed. Regarding the composite process, the interlayer residual stress generated by traditional hot-pressing composite lamination is a key factor in the subsequent deformation of the panel, necessitating innovative composite process innovations to improve composite stability. These core issues have become key bottlenecks hindering the development of high-performance APCs for interior decoration. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems in the existing technology and to provide an aluminum-plastic composite panel for interior decoration and a preparation method thereof.

[0004] The objectives of the present invention can be achieved through the following technical solutions: an aluminum-plastic composite panel for interior decoration, comprising a chromium-free passivated back aluminum alloy plate, wherein the lower surface of the chromium-free passivated back aluminum alloy plate is provided with an impact-resistant epoxy primer protective layer; the upper surface of the chromium-free passivated back aluminum alloy plate is connected to the lower surface of an LDPE flame-retardant core layer via a lower adhesive film; the upper surface of the LDPE flame-retardant core layer is connected to the lower surface of the chromium-free passivated surface aluminum alloy plate via an upper adhesive film; the lower adhesive film and the upper adhesive film are both composite adhesive films, and the composite adhesive film comprises a metal interface adhesive layer, an anti-migration stable intermediate adhesive layer, and a core material interface flame-retardant adhesive layer; the upper surface of the chromium-free passivated surface aluminum alloy plate is stacked in sequence from bottom to top: a flexible epoxy interface bonding transition layer, a pattern decorative layer, and a PVDF protective layer.

[0005] A method for preparing an aluminum-plastic composite panel for interior decoration, comprising the following steps:

[0006] S1 chromium-free passivation treatment: The back aluminum alloy plate and the front aluminum alloy plate are subjected to chromium-free passivation treatment respectively to obtain a chromium-free passivated back aluminum alloy plate and a chromium-free passivated front aluminum alloy plate; both the back aluminum alloy plate and the front aluminum alloy plate are 3003 aluminum alloy plates; the chromium-free passivation treatment includes ultrasonic weak alkaline degreasing and degreasing, the first countercurrent water washing, polishing, the second countercurrent water washing, zirconium-based passivation, low-conductivity water washing and drying steps;

[0007] Optimization plan for chromium-free passivation process specifically for 3003 aluminum alloy: For degreasing and cleaning: Current problems: In actual production, since 3003 aluminum alloy contains alloying elements such as manganese and copper, there are local oxidation-rich areas on the surface. When degreasing is not thorough, the oil residue will hinder the uniform effect of the degreasing liquid on such areas, resulting in spotty loss or uneven adhesion of the subsequent passivation film; Optimization plan for weak alkaline degreasing cleaning liquid specifically for 3003 aluminum alloy: In ultrasonic weak alkaline degreasing and oil removal, the degreasing liquid includes: 15-20g / L Texent610A surfactant, 8-10g / L AEO-9 surfactant, 6.0-7.0g / L sodium gluconate, 6.0-7.0g / L sodium silicate, 9-11g / L sodium carbonate and deionized water; sodium hydroxide is used as the pH regulator; the pH value of the degreasing liquid is 9.0-10.0. This formula achieves ultra-low interfacial tension through a combination of surfactants, a dual alkaline agent + buffer to stabilize the process window, a chelating agent to target and block alloy-interfering ions, and combined with physical strengthening through ultrasonic cavitation, it solves the degreasing bottleneck problem of 3003 aluminum alloy in the pre-treatment of chromium-free passivation. The specific reasons are as follows: Texent610A surfactant: It performs excellently in alkaline degreasing and cleaning of 3003 aluminum alloy. Its main advantages include: High-efficiency oil removal: Texent610A has a fast oil removal speed and strong oil removal ability, and its effect is more obvious than NP-10, isomeric alcohol ether 1308, Berol226SA, etc.; Low corrosion: Texent610A has low corrosion to aluminum alloy and basically does not corrode metal workpieces; Environmental performance: Texent610A does not contain phosphorus and has good biodegradability, meeting environmental protection requirements. AEO-9 (fatty alcohol polyoxyethylene ether nonionic surfactant): Emulsification and solubilization: The nine EO groups form a hydration layer, which encapsulates oil to form micelles, solving the problem of high-viscosity stamping oil residue. Synergistic effect: After compounding with Texent610A, efficient degreasing can be achieved at low concentrations, which can reduce the usage of Texent610A; Sodium gluconate: complex metal ions: preferentially chelate Mn dissolved in 3003 aluminum alloy 2+ 、Cu 2+Plasma prevents the formation of insoluble soap scum on the surface (addressing spot defects caused by incomplete degreasing). Stabilized bath: Inhibits hard water ion scaling and maintains surfactant activity. Alkali agent combination: Sodium hydroxide + sodium carbonate + sodium silicate: Sodium hydroxide (primary degreasing alkali source): Provides an alkaline environment (pH 9.0-10.0) to saponify ester oils; Sodium carbonate (pH buffer): Maintains pH stability; Sodium silicate (corrosion inhibitor): Forms a colloidal film on the aluminum surface to prevent excessive alkaline corrosion. Ultrasonic enhanced cleaning (40-60kHz): Cavitation effect: Microjets impact the surface oil film, removing oil contamination from micropores (addressing uneven degreasing of complex structures). Key process parameter control: pH: Strictly controlled between 9.0–10.0 (optimal midpoint 9.5); Control method: Automatically add NaOH with real-time monitoring and feedback. Temperature: 50–60°C; Temperatures below 50°C reduce reaction rate, while temperatures above 60°C increase the risk of aluminum corrosion. Ultrasonic parameters: Frequency: 40±2kHz (optimal cavitation intensity) Power density: ≥0.5W / cm 2 (Ensure micro-pore cleaning) Time: 3–5 min (adjusted according to the degree of oil contamination) Water quality requirements: Countercurrent water washing: conductivity ≤ 50 μS / cm;

[0008] For polishing: Deoxidizer150-40 polishing agent is used. The polishing agent is suitable for post-alkali washing treatment of aluminum and aluminum alloys. It can effectively remove surface stains and oxides, making the surface smooth. It is simple to operate and takes a short time. Compared with other products on the market, it has a good polishing effect on 3003 aluminum alloy.

[0009] Current Issues: Core Issues and Mechanism Analysis of Chromium-Free Passivation of 3003 Aluminum Alloy: As an Al-Mn alloy, 3003 aluminum alloy faces unique challenges during chromium-free passivation. These challenges stem from its unique microstructure and electrochemical properties. Through in-depth analysis, we found that the main issues focus on: Manganese segregation and the effect of second-phase particles: Manganese in 3003 aluminum alloy forms Al6Mn intermetallic compounds during processing and heat treatment. These second-phase particles are dispersed and range in size from hundreds of nanometers to several microns. These particles have a significant potential difference from the aluminum matrix. During the passivation process, this potential difference leads to uneven local etching and significantly lower zirconium content in Mn-rich areas. The existing process is also inadequately adaptable. The current Alodine 4830 / 4831 standard process for 3003 aluminum alloys is primarily limited by insufficient film formation in the Mn zone and the standard process requirement of <10 ppm iron ions, which does not account for the effects of manganese ions. We have proposed a comprehensive optimization solution based on the Alodine 4830 / 4831 system. By adding additives, we effectively address the issues of manganese segregation and uneven film formation. By appropriately reducing the amount of Alodine 4831 used and adding potassium fluorozirconate to create a slow-release system, we can slowly release ZrF62- to extend film formation time in the Mn zone and address insufficient film formation in this area. Citric acid selectively etches the Al6Mn oxide film, increasing Zr adsorption sites. Succinic acid forms a chelate with Mn, preventing it from consuming free acid or co-depositing in the passivation film, thereby improving the bath's manganese tolerance. In the original process, 5-7.5L of Alodine4830 and 12.5L of Alodine4831 were added to 1000L of bath liquid. The process was optimized to add 6-6.5L of Alodine4830, 12L of Alodine4831, 0.5-0.6kg of citric acid, 0.3-0.4kg of succinic acid and 0.85-0.9kg of potassium fluozirconate to 1000L of bath liquid. Through the triple effects of slow-release zirconium source + selective etching + manganese chelation, the manganese segregation problem of 3003 aluminum alloy is solved in a targeted manner, while being compatible with the original environmental protection and process simplicity of the Alodine system.

[0010] In low conductivity water washing, water with a conductivity of less than 25μS / cm is used as the cleaning agent;

[0011] S2 primer coating: coating the lower surface of the chromium-free passivated back aluminum alloy plate with an impact-resistant epoxy resin paint as an impact-resistant epoxy primer protective layer to obtain a pre-composite back aluminum alloy plate;

[0012] Current Problem: Traditional protective coatings often prioritize topcoat over primer, or appearance over undercoat. They often focus solely on corrosion protection while neglecting impact resistance. After unpacking, scratches from lifting and transport, indentations from workers, and cracks from nailing / drilling holes can easily become corrosion initiation points, reducing customer satisfaction. DreamCover221, a special aluminum alloy epoxy resin coating with impact and corrosion resistance, is specifically designed for aluminum alloys. It utilizes a reverse roll coating process and incorporates 2-3% of the silane coupling agent KH560 (to enhance chemical bonding with the passivation layer). This aluminum alloy primer is chosen for the following reasons: DreamCover221 is a two-component, air-drying coating composed of epoxy resin, various pigments, wear-resistant fillers, additives, and solvents (one component) and a special curing agent (the other component). The resulting film is tough, exhibiting excellent adhesion and impact resistance. The paint film has an outstanding anti-rust effect and also has good water resistance, oil resistance and solvent resistance. It does not contain heavy metals and is beneficial to environmental protection.

[0013] S3: preparing a functional coating: sequentially preparing a flexible epoxy interface bonding transition layer, a patterned decorative layer, and a PVDF protective layer on the upper surface of the chromium-free passivated aluminum alloy plate to obtain a pre-composite aluminum alloy plate;

[0014] When preparing the flexible epoxy interface bonding transition layer, bisphenol A epoxy resin and a flexible long-chain epoxy addition-modified polyamide curing agent are used. To enhance the adhesion between the surface coating and the metal substrate, a primer is applied to the chromium-free passivated aluminum alloy surface as a transition layer. The primer is made of epoxy resin, which has excellent corrosion resistance and adhesion, laying a good foundation for subsequent coatings. Epoxy coatings were chosen because the Alodine 4830 / 4831 passivation layer is very thin, but has a dense structure and is firmly bonded to the metal substrate. Its surface micro-roughness is sufficient to provide a certain degree of mechanical anchoring. When the epoxy primer cures, its active groups can chemically react with the passivation layer to form covalent bonds. Curing shrinkage is controllable: the epoxy resin curing shrinkage rate is low (2-5%), which reduces the damage to the interface caused by internal stress. The purpose of using flexible long-chain epoxy addition modified polyamide is: stress buffering: absorbing the thermal stress between the aluminum plate and the subsequent coating through the flexible cross-linking network, offsetting the interface stress caused by the difference in thermal expansion coefficient between the aluminum plate and the subsequent coating; preventing cracking. Interface enhancement: the epoxy group forms a chemical bond (such as -Al-O- bond) with the passivation layer to protect the aluminum alloy substrate. Flexible support: provides a base for the pattern decoration layer (thermal transfer ink) to avoid brittle fracture. For example, using Versamid TM115 modified curing agent can match various types of bisphenol A epoxy resins. The product is non-toxic and meets environmental protection requirements. During the coating process, a precision roller coater (roller gap accuracy of ±1μm) is used to apply a single coat on the surface of the chromium-free passivated aluminum alloy plate. After coating, it is leveled for 5 minutes (ambient temperature) and then cured.

[0015] When preparing the pattern decoration layer, a vacuum thermal transfer process is adopted. The structure of the thermal transfer film used is PET base film, silicone release layer, pattern printing layer and epoxy modified polyurethane hot melt adhesive layer from top to bottom. The vacuum thermal transfer process is used to prepare the pattern decoration layer: The reasons are as follows: Excellent decorative effect and pattern diversity: High realism: It can perfectly replicate various complex textures and patterns, such as wood grain, stone grain (marble, granite), metal wire drawing, cloth grain, abstract patterns, etc. The effect is extremely realistic and can almost be mistaken for the real thing. Rich pattern selection: The design and printing of the transfer film are not subject to too many restrictions, and can provide an extremely wide range of design options to meet diverse market needs and personalized customization. Continuous production: During the vacuum hot pressing process,

[0016] The process can be completed in one step, greatly simplifying the production process and improving efficiency. It is suitable for continuous coating production lines for aluminum coils, with high production efficiency and suitability for large-scale production. The specific process is as follows: Pretreatment: After the epoxy flexible interface bonding transition layer is subjected to electrostatic dust removal treatment; Transfer film preparation: A silicone release layer, a pattern decoration layer, and a hot melt adhesive layer are sequentially formed on the PET base film to form the transfer film; PET base film: Mechanical support and heat-resistant carrier (thickness not less than 42μm), pattern decoration layer (pattern, customized according to customer requirements, gravure printing, ΔE < 1.0), hiding power (titanium dioxide / iron-based and other environmentally friendly pigments), precise control of coating gloss; Hot melt adhesive layer: Epoxy-modified polyurethane hot melt adhesive (PUR), for example, TECHNOMELT PUR4663. This type of hot melt adhesive has high initial strength and can quickly generate a certain degree of adhesion when in contact with epoxy resin primer, achieving initial fixation. After cooling, it undergoes an additional cross-linking reaction, further improving the bonding strength and cohesive strength, making the connection with the epoxy resin primer more stable; Vacuum bonding: Place in a vacuum hot press and evacuate to ≤10-2Pa; Hot press transfer: Heat to the preset temperature, apply 0.5-1.5MPa pressure, and maintain heat and pressure for 30-120 seconds; Release separation: After cooling, release the vacuum and peel off the release film;

[0017] The PVDF protective layer is prepared using a two-pass coating-precuring and mirror roller calendering-main curing-cooling process; PVDF resin: F201 type; thermoplastic acrylic resin: molecular weight: 70,000-90,000 g / mole; acid value <2 mgKOH / g; chromaticity (Fe-Co) ≤1;

[0018] F201 PVDF and thermoplastic acrylic resin are mixed in a mass ratio of 7:3 as the resin base material. Based on the percentage of the resin base material mass, the following functional additives are added: 0.3-0.4% of polydimethylsiloxane-b-polyoxyethylene, 0.5-0.7% of surface-modified fumed nano-silica, 0.4-0.5% of surface-modified potassium titanate whiskers, 0.3-0.4% of surface-modified γ-phase nano-alumina, 0.3-0.4% of hindered amine and triazine compound light stabilizers, and 0.09-0.12% of acrylate or polyacrylate leveling agents; mirror roller calendering: eliminates orange peel / pinholes, makes the surface extremely smooth, improves gloss consistency and enhances surface density.

[0019] Traditional PVDF coatings have the following defects: roller coating is prone to produce orange peel and pinholes, affecting gloss uniformity (gloss deviation > 5GU); the ultraviolet band of indoor light sources (LED / fluorescent lamps) causes yellowing of acrylic resin and breakage of PVDF molecular chains; performance imbalance: increased hardness often sacrifices flexibility, and it is impossible to simultaneously meet 2T flexibility and 2H hardness requirements.

[0020] F201 PVDF Resin: High Purity: ≥99.5% purity. This high purity reduces the adverse effects of impurities during application, ensuring product quality and performance stability. Excellent dispersibility: Dispersed fineness ≤25μm. This property allows for better mixing with other ingredients in applications such as coatings, forming a uniform coating, thereby improving coating performance and appearance. Thermoplastic Acrylic Resin: A molecular weight of 70,000-90,000 g / mole is required to balance mechanical properties and processability. A too low molecular weight results in insufficient film hardness and scratch resistance, while a too high molecular weight significantly increases solution viscosity, reduces solids content, and affects leveling during the coating process. Acid Value <2mgKOH / g; Chemical Resistance: Acrylic resins with high acid values ​​can reduce their chemical resistance. This is because the double bonds in high acid values ​​are prone to ring-opening reactions, reducing their resistance to acids, alkalis, and chemical corrosion. Transparency: Transparency is a key indicator of acrylic resin quality. Acrylic resins with high acid values ​​will experience a decrease in transparency due to changes in their molecular structure. Viscosity: The acid value of acrylic resin is inversely proportional to its viscosity. The higher the acid value, the fewer ester groups on the molecular chain, resulting in greater distances between adjacent double bonds and a relatively low degree of polymerization, leading to a corresponding decrease in molecular weight. This decrease in molecular weight leads to a decrease in viscosity. BN44 thermoplastic acrylic resin and F201 PVDF resin can be used as the resin base material in a mass ratio of 3:7.

[0021] The combination of BN44 thermoplastic acrylic resin and F201 PVDF is a conventional combination frequently used in the industry. The specific preparation method of the coating will not be described in detail here. Compared with the simple use of PVDF-based coatings, the main reason for the good effect is the added functional additives: polydimethylsiloxane-b-polyoxyethylene: it has excellent hydrophobicity, heat resistance and chemical stability, giving the material good mechanical strength and weather resistance, low surface tension and excellent lubricating properties make it an ideal lubricant and antifouling agent, effectively preventing the adhesion of oil stains and easy to clean. Surface modified fumed nano-silica is specifically hexamethyldisilazane surface modified fumed nano-silica; surface modification is used to improve dispersibility in coatings; function: has self-cleaning function, can refine coating surface texture and regulate glossiness, act as a thixotropic agent, regulate coating viscosity and fluidity, prevent sagging or sedimentation during construction, and improve coating uniformity; surface modified potassium titanate whiskers are specifically isopropyl tris (dioctyl pyrophosphate acyloxy) titanate surface modified potassium titanate crystals; surface modification improves dispersibility, function: improves scratch resistance and maintains toughness at the same time; surface modified γ-phase nano-alumina: surface modification is used to improve dispersibility, function: enhance surface hardness; compound light stabilizer: hindered amine light stabilizer model is 111, triazine light stabilizer model is 1577, according to the weight ratio, hindered amine light stabilizer: triazine light stabilizer is 1:2.5-3; specially designed for indoor environment: UV threat and spectral characteristics of indoor light sources: LED lamps: 395-410nm trace leakage, triggering PVDF molecular chain breakage (photooxidation reaction); fluorescent lamps: 300-400nm (main peak 365nm) accelerates the yellowing of acrylic resin; halogen lamps / incandescent lamps: 300-500nm continuous spectrum thermal radiation + UV synergistically lead to loss of light; PVDF (polyvinylidene fluoride) itself has excellent chemical stability and weather resistance, but its surface may produce microcracks due to processing residues or long-term use. It has a broad spectrum absorption capacity and reduces direct damage to PVDF. Free Radical Capture: Nitroxides capture alkyl and alkoxy radicals, blocking the chain reaction. Compounding creates a dual absorption and scavenging defense, protecting the PVDF coating and maintaining the color of the decorative layer. Acrylate or polyacrylic resin-based leveling agents: Highly effective leveling: Significantly reduces surface tension, improving coating leveling and minimizing surface defects such as orange peel. Recoatability: Does not affect intercoat adhesion, making it suitable for multi-layer coating systems. Low Foaming: Effectively reduces bubble generation during the coating process, improving coating quality. Mirror Roller Calendering Process Requirements: Long-wave leveling capability: By adjusting the local surface tension gradient of the coating, it eliminates orange peel defects caused by mechanical shear during roller coating, meeting the stringent surface flatness requirements of roller calendering. Thixotropy Control: Viscosity decreases with increasing shear rate (shear thinning), facilitating roller coating spreading; viscosity rebounds at rest to prevent sagging. Surface Density and Chemical Resistance: Molecular chain segments are embedded into the PVDF crystalline domains, enhancing coating density. Its hydrophobic groups reduce surface energy and inhibit the adhesion of contaminants. In contrast, silicone leveling agents can cause uneven surface energy due to migration, reducing chemical resistance. For example, choose BYK-361N acrylate leveling agent or Flow300 polyacrylate leveling agent: they significantly improve flow and clarity in clearcoats, exhibit high compatibility with long-wave effects during spray application (reducing the risk of fogging), and are thermally stable, providing excellent recoatability and defoaming properties.

[0022] S4 preparation of LDPE flame retardant core layer: raw material pretreatment, segmented feeding and mixing, filtration, melt gear pump pressure stabilization, sheet extrusion, roller shaping and cooling operations are carried out in sequence to prepare the LDPE flame retardant core layer;

[0023] In the segmented feeding and mixing, the following settings are made: Section 1: preliminary melting section: a deep groove thread device is used for conveying; LDPE, mixed resin masterbatch, calcium stearate, EBS, and compound antioxidant are added through the main feeding port, partially melted by temperature control, and a viscoelastic continuous phase containing a solid particle carrier is formed; the resin used in the mixed resin masterbatch includes LDPE, ionic ethylene-methacrylic acid copolymer resin, EVA, and LDPE-g-MAH, which are prepared by a co-blending extrusion process; the compound antioxidant includes hindered phenol antioxidants and phosphite antioxidants; Section 2: strong shear melting and dispersion section : Add surface-modified flame-retardant fillers, which include surface-modified magnesium hydroxide, surface-modified aluminum hydroxide, and surface-modified magnesium-aluminum layered double hydroxide; Section 3: Reverse thread devolatilization section: Inject molten oxidized polyethylene wax at the beginning of the reverse thread devolatilization section; Configure a two-stage vacuum system and reverse thread elements; Form a melt reflow zone through the reverse thread elements; Station 4: Weak kneading and mixing section: Add surface-modified APP / MCA compound flame retardant additives and surface-modified zinc borate; Section 5: Low shear homogenization section: Add molten PTFE and surface-modified short glass fibers;

[0024] According to the weight ratio, LDPE: mixed masterbatch: calcium stearate: EBS: compound antioxidant: surface-modified magnesium hydroxide: surface-modified aluminum hydroxide: surface-modified magnesium-aluminum layered double hydroxide: oxidized polyethylene wax: surface-modified APP / MCA compound flame retardant additive: surface-modified zinc borate: PTFE: surface-modified short glass fiber is 55-60:17-23:0.2-0.25:0.2-0.3:0.4-0.5:25-30:15-20:5-8:0.45-0.6:10-12:4-5:0.8-1.2:2-3;

[0025] In the mixed resin masterbatch, the weight ratio of LDPE: ionic ethylene-methacrylic acid copolymer resin: EVA: LDPE-g-MAH is 30-32:17.5-18:32-35:17.5-20, and the ionic ethylene-methacrylic acid copolymer resin is Surlyn 1855 resin. The purpose of using the mixed resin masterbatch is to uniformly disperse the functional resins, avoid agglomeration, and better perform their functions.

[0026] The resin raw materials used are those commonly used in the production of aluminum-plastic composite panels. Manufacturers such as Yanshan Petrochemical, Qilu Petrochemical, or Yangzi Petrochemical are selected. When making the selection, the market price is mainly used as the benchmark. Preferably, LDPE: melt index MI = 2-10g / 10min; LDPE-g-MAH grafting rate is not less than 0.8%; EVA: VA content is 18-28%; Special note: MI is a key indicator for measuring melt fluidity. The melt index of LDPE is compatible with the flame-retardant core layer preparation process: balance between fluidity and dispersion: Too low melt index: leads to excessive mixing torque and increased energy consumption; hinders melt reflux in the devolatilization stage, reducing the efficiency of volatile removal; increases the gear pump delivery pressure, affecting the pressure stabilization accuracy (±0.3% fluctuation requirement). Too high melt index: insufficient melt strength, unable to stably support short glass fibers; edge shrinkage is prone to occur under high filling (increasing the difficulty of die lip temperature control compensation); cost balance: LDPE with an MI in the range of 2-10g / 10min is in sufficient supply and relatively stable in price. The choice of LDPE as the main resin for the flame retardant core layer is also based on cost considerations, as LDPE is cheap.

[0027] In the compound antioxidant, the mass ratio of hindered phenol antioxidant 1010 to phosphite antioxidant 168 is 1:1-1.2;

[0028] In the surface-modified flame-retardant filler, at least one of γ-methacryloxypropyltrimethoxysilane and titanate coupling agent LK-101 is used to modify the surface of aluminum hydroxide, magnesium hydroxide, and magnesium-aluminum layered double hydroxide; the particle size of the magnesium hydroxide is 5-10 μm; the particle size of the aluminum hydroxide is 5-10 μm; and in the magnesium-aluminum layered double hydroxide, the magnesium content: aluminum content is 2-3:1;

[0029] The surface-modified APP / MCA compound flame retardant additive is specifically a surface-modified APP / MCA compound flame retardant additive of γ-methacryloxypropyltrimethoxysilane, wherein the weight ratio of APP:MCA is 2.5-3:1;

[0030] The surface-modified zinc borate is specifically zinc borate surface-modified with DL-411 aluminate coupling agent;

[0031] The surface-modified short glass fiber is specifically a short glass fiber surface-modified with γ-methacryloxypropyltrimethoxysilane; the short glass fiber has a length of 3-7 mm and an aspect ratio of 20-25;

[0032] In deep groove thread devices, the groove depth-to-width ratio is ≥1.5, achieving gentle conveying;

[0033] In the strong shearing and dispersing section, kneading block elements with a staggered angle of 45° are configured;

[0034] In the weak kneading and mixing section of the fourth station, neutral diamond kneading block elements are used;

[0035] In the low shear homogenization section of the fifth stage, shallow groove thin-walled threaded elements are configured, and the depth-to-width ratio of the thread groove is ≤0.8.

[0036] In filtration, a double-column screen-changing filter device is used;

[0037] In the melt gear pump pressure stabilization, dual-stage voltage stabilization technology is adopted. The main pump pressure stabilization: a high-precision involute gear pump is used, and the outlet pressure fluctuation is ≤±0.3%, ensuring the stability of the melt flow. Pulsation damper: a resonant pulsation damper is added at the gear pump outlet. The piezoelectric ceramic sensor monitors the pressure fluctuation in real time and adjusts the gear speed through feedback. Temperature control optimization: the gear pump adopts zoned temperature control, and the contact surface between the pump body and the melt is sprayed with a nano-zirconia thermal insulation coating.

[0038] During extrusion, the die head adopts a coat-hanger-shaped flow channel structure, with the inner wall of the flow channel mirror-polished and coated with a corrosion-resistant alloy layer. The interior of the die head is divided into the following sections along the melt flow direction: a conical diffusion zone: the flow channel cross-section gradually expands to accommodate the melt from the melt gear pump; a flow control distribution zone: a built-in adjustable flow block with a hyperbolic profile design; a steady flow convergence zone: the flow channel cross-section gradually decreases, and the surface is provided with a thermal insulation coating; a die lip zone: the die lip outlet is connected to the thickness pre-compensation device, and the discharge gap can be adjusted online; the die lip zone has three independent temperature control sections in the transverse direction, so that the temperature on both sides is 2-5°C higher than that in the center to suppress edge shrinkage effects.

[0039] In roller shaping, a three-roll calender is used, and a melt elastic pre-relaxation zone is added at the roller inlet to avoid warping caused by fiber orientation;

[0040] During cooling, there are contact-type gradient slow cooling section and forced air cooling section. In the contact-type gradient slow cooling section, cooling roller device is adopted for cooling; in the forced air cooling section, multi-bellows turbulent cooling system is adopted, and an asymmetric cooling strategy is adopted. The lower layer wind pressure is greater than the upper layer wind pressure to compensate for the curvature deformation caused by the deadweight of the core layer. Annular gap air nozzles are added on both sides to suppress edge curling.

[0041] The core of this solution lies in systematically addressing the aforementioned issues through the synergistic effects of precise material formulation design, flame retardant surface modification, staged process optimization, and innovative equipment structure. Staged feeding and structured mixing (core advantage): This differs from conventional methods, which typically add all or most of the materials to the mixing equipment (such as a twin-screw extruder) at once or in batches, resulting in a relatively extensive mixing and dispersion process. Advantages of this solution: Stage 1 (initial melting): Initially forms a continuous polymer phase (LDPE + mixed resin masterbatch + additives), establishing melt strength and viscoelasticity, laying the foundation for subsequent high-filling. The "viscoelastic continuous phase containing a solid particle carrier" is crucial, providing a carrier to ensure effective dispersion of the subsequent flame retardant addition. Stage 2 (high shear dispersion): Addition of the surface-modified primary flame retardant filler. A 45° staggered kneading block provides high shear forces, specifically designed for the robust dispersion of easily agglomerated inorganic hydroxides (Mg(OH)2, Al(OH)3, LDHs). This allows the melt to withstand high shear without breaking. Section Three (Reverse Thread Devolatilization): A key innovative section, reverse thread element + melt reflow zone: forces melt reflow, extends residence time, and enhances devolatilization. Two-stage vacuum system: efficiently removes water vapor, air, and other volatiles generated by flame retardant dehydration, significantly reducing bubbles. Injection of molten oxidized polyethylene wax: injected at the beginning of devolatilization, it plays a role in lubrication, improving flow, and assisting demolding, while avoiding premature addition affecting dispersion or late addition causing uneven dispersion. Section Four (Weak Kneading and Mixing): Add surface-modified APP / MCA compound flame retardant and surface-modified zinc borate. Neutral diamond-shaped kneading blocks are used to provide gentle shear to prevent secondary damage to the already dispersed main flame retardant, while ensuring that APP / MCA / zinc borate are evenly mixed without excessive shear decomposition (APP is sensitive to shear and high temperature). Section Five (Low Shear Homogenization): Add PTFE (to improve flame retardancy and anti-drip properties) and surface-modified short glass fiber (for reinforcement). Shallow groove thin-walled threaded elements (depth-to-width ratio ≤ 0.8) are used to achieve low-shear, high-conveying efficiency homogenization, avoiding excessive fiber breakage and PTFE agglomeration, while preventing the melt from overheating again. Advantages: Avoid premature addition of flame retardants leading to decomposition; ensure that flame retardants with different properties, different particle sizes, and different addition amounts are dispersed in the most appropriate manner (shear strength) at the most appropriate stage; optimize the melt state, reduce energy consumption and degradation; maximize the devolatilization effect. Comprehensive flame retardant surface modification (core advantage): Difference from conventional: Conventional core layers may mainly use LDPE, or simply blend a small amount of other resins. Advantages of this solution: Contains LDPE, Surlyn1855 (ionic ethylene-methacrylic acid copolymer), EVA, LDPE-g-MAH. Surlyn1855: Provides excellent toughness, impact resistance, and adhesion. Its ionic cross-linking properties can enhance melt strength. EVA: Improves flexibility and compatibility with flame retardants.LDPE-g-MAH: As a compatibilizer / extender, its anhydride groups react with the surface hydroxyl groups of flame retardants (especially those modified with silanes / titanates). It also interacts better with Surlyn / EVA, significantly enhancing overall compatibility and interfacial adhesion. Effect: Compared to pure LDPE, this composite matrix exhibits improved melt strength, toughness, flexibility, and compatibility with flame retardants. This provides a superior foundation for highly filled flame retardant systems and is key to balancing high flame retardancy with good mechanical properties. Precision extrusion and pressure stabilization system (key advantage):

[0042] Two-stage voltage stabilization technology (innovation): High-precision involute gear pump (fluctuation ≤±0.3%): provides extremely stable melt flow, which is the basis for subsequent stable extrusion. Resonant pulsation damper + piezoelectric ceramic feedback control: actively eliminates the tiny pulsations inherent in the gear pump to achieve ultra-stable melt pressure output, which is crucial for the uniform extrusion of highly filled materials. Zoned temperature control + nano-zirconia thermal insulation coating: precisely controls the pump body temperature, reduces differences in melt thermal history, and prevents local overheating. Effect: Ensures that the melt pressure, flow, and temperature entering the die are extremely stable, which is a prerequisite for achieving high-precision and high-uniformity sheet extrusion. Optimized die design (important advantage): Different from conventional: Conventional may use a simple hanger-type or T-type die, and the temperature control may not be precise enough. Advantages of this solution: Hanger-type flow channel + mirror polishing + corrosion-resistant alloy coating: ensures that the flow channel is smooth, wear-resistant, and resistant to flame retardant corrosion, reducing material hanging and degradation. Zoned Design (Conical Diffusion / Flow Distribution / Stable Flow Bunching / Die Lip): A double-curvature flow block finely adjusts lateral flow distribution to compensate for uneven flow caused by the melt's viscoelasticity. A thermal insulation coating maintains a stable temperature in the steady flow zone. A thickness pre-compensation device and online die lip gap adjustment enable high-precision thickness control. Three independent temperature control zones in the die lip area (2-5°C higher on both sides) actively compensate for melt "necking" at the die lip exit, effectively suppressing sheet edge thinning and shrinkage.

[0043] Effect: Achieve highly uniform transverse thickness of the sheet, flat edges, smooth surface and no defects. Roller shaping and cooling process optimization (important advantage): Difference from conventional: Conventional three-roll calendering may directly contact the high-temperature melt, and the cooling is more uniform. Advantages of this solution: Melt elastic pre-relaxation zone: Allow the melt to relax moderately before entering the calendering roller to release internal stress and reduce warping deformation caused by fiber orientation and molecular orientation. Gradient slow cooling + forced air cooling: Contact gradient slow cooling (cooling roller): First pass through relatively mild roller contact cooling to avoid excessive internal stress caused by sudden cooling. Forced air cooling (multi-bellows turbulent cooling): Asymmetric cooling (lower layer wind pressure > upper layer): Actively compensate for the curvature deformation tendency of the sheet caused by its own weight, and maintain the flatness of the sheet. Annular gap nozzle (on both sides): Precise and intensive cooling of the sheet edge, effectively suppressing edge curling. Effect: Minimize the internal stress and warping deformation of the sheet to ensure the high flatness of the final product.

[0044] Compared to conventional LDPE flame-retardant core preparation methods, this technical solution is a highly refined, systematic, and innovative one. Through in-depth collaborative design of materials, processes, and equipment, specifically core technologies such as segmented structured mixing, a composite resin matrix, two-stage precision voltage stabilization, die temperature control and compensation, and stress-controlled cooling, it successfully addresses the key challenges of highly filled B1-grade LDPE flame-retardant core layers in terms of dispersibility, compatibility, processability, mechanical property retention, and flame retardant efficiency.

[0045] S5 Preparation of composite adhesive film: The composite adhesive film is prepared using a three-layer co-extrusion process; the resins used in the metal interface adhesive layer include MAH-g-PE, EVA, and LDPE; the resin used in the anti-migration stabilization intermediate adhesive layer is bimodal LLDPE, and the anti-migration agent is polydopamine-coated nano-silica; the resins used in the core material interface flame-retardant adhesive layer include mLLDPE, LDPE-g-MAH, and EVA, with surface-modified magnesium hydroxide added as a flame retardant additive;

[0046] The resins used are in a weight ratio of 50-55:20-25:20-25 for the metal interface bonding layer and 35-40:25-30:35-40:6-8 for mLLDPE:LDPE-g-MAH:EVA:surface-modified magnesium hydroxide for the core material interface flame retardant bonding layer.

[0047] The grafting rate of MAH-g-PE is greater than 1%. The same model is used for LDPE, LDPE-g-MAH and EVA as for the flame-retardant core layer. On the premise of meeting the viscosity, chemical compatibility, interface diffusion enhancement, thermal expansion matching, etc. can be achieved.

[0048] The comprehensive performance of aluminum-plastic composite panels depends largely on the structural design and material selection of the composite adhesive film. As the key interface layer connecting the chromium-free passivated aluminum alloy plate and the flame-retardant core layer, the adhesive film needs to meet multiple functional requirements simultaneously: on the aluminum alloy plate side, it must form a strong bond with the fluorine-containing zirconate conversion film; on the core material side, it needs to achieve a highly compatible bond with the LDPE layer containing a large amount of flame-retardant filler; in addition, it must adapt to the high temperature and high pressure conditions of the hot pressing composite process. Through an in-depth analysis of the structure of conventional adhesive films, combined with the chromium-free passivation process and the characteristics of the flame-retardant core layer, an optimized three-layer composite adhesive film structure is proposed, aiming to comprehensively improve the interfacial bonding strength and comprehensive performance of aluminum-plastic composite panels. In the current structural design of high-performance aluminum-plastic composite panels, the chromium-free passivated aluminum alloy plate and the LDPE flame-retardant core layer are firmly connected through the composite adhesive film. The aluminum alloy plate forms a micro-nanoscale conversion film (mainly composed of fluorozirconate) after passivation treatment, while the flame-retardant core layer contains a flame-retardant system such as a highly filled modified hydroxide, APP / MCA, etc. This composition difference leads to significant differences in the chemical properties, surface energy, and thermal expansion coefficient of the interfaces on both sides. It requires that the composite adhesive film must adopt a gradient design to achieve stable and reliable interlayer bonding. Based on the characteristics of the passivation layer, the metal interface adhesive layer must meet the following adaptability requirements: Chemical bonding ability: It must contain sufficient polar groups such as anhydride, epoxy, or carboxyl groups to form a covalent bond with the passivation film. The anhydride group of maleic anhydride grafted polyethylene can undergo a cyclic esterification reaction with the zirconium hydroxyl group to form a strong chemical bond. In the metal interface bonding layer, MAH-g-PE with a grafting rate greater than 1.0% is used: its anhydride group can form imide bonds and ester bonds with the passivation film, significantly improving the interface bonding strength; EVA provides chain segment movement ability, adapts to the thermal expansion difference between the aluminum alloy and the plastic core material, and prevents thermal stress from causing interface peeling; LDPE is used to balance the overall shrinkage rate; in this formula, a better balance is achieved through chemical bond strength, cohesive strength and toughness of the bonding layer, thermal stability, and resistance to thermal stress. Anti-migration stable intermediate bonding layer: Main material: bimodal LLDPE, bimodal distribution (high molecular weight provides mechanical strength + low molecular weight improves processing fluidity), such as Borouge Anbiq TM FM1810; anti-migration agent: polydopamine-coated nano-silica; core material interface flame-retardant bonding layer: mLLDPE: narrow molecular weight distribution and uniform branched structure prevent film tearing during hot pressing and lamination, which is impossible for LLDPE; uniform molecular chain structure and excellent melt strength form a diffusion entanglement interface; LDPE-g-MAH, its anhydride group combines with the flame-retardant filler in the core material; EVA: reduces the modulus and matches the stress-strain behavior of the core material. Flame retardant: surface-modified magnesium hydroxide forms a synergistic relationship with the core material flame retardant system to improve the interface flame retardancy, while also serving as a reinforcing filler to increase the cohesive strength of the bonding layer.

[0049] S6 pre-lamination: After surface treatment of the flame retardant core layer, composite adhesive films are laminated on the upper and lower surfaces of the LDPE flame retardant core layer to obtain a pre-laminated flame retardant core layer;

[0050] S7 hot pressing composite: The pre-composite back aluminum alloy plate, pre-composite flame-retardant core layer and pre-composite face aluminum alloy plate are stacked and assembled in order from bottom to top, and then hot pressing composite, edge sealing and packaging operations are carried out in sequence to obtain the aluminum-plastic composite panel; the staged hot pressing composite includes a preheating stage of exhaust and low-temperature initial bonding, a main composite stage of dynamic heating and pressurization, a cooling stage of stress relaxation and slow cooling, and a constant pressure aging curing stage.

[0051] During the preheating stage of exhaust and low-temperature initial bonding, a pulse pressurized vacuum pre-compression exhaust method is adopted, and low-frequency mechanical vibration is applied simultaneously to assist exhaust and improve initial bonding strength.

[0052] During the final packaging, the protective film used for the aluminum-plastic composite panel is a BOPET protective film coated with a silicone release agent.

[0053] The present invention has the following beneficial effects: Environmental performance: The chromate passivation process, which contains highly toxic hexavalent chromium, is completely abandoned. A specially formulated chromium-free passivation system, combined with ultrasonic weak alkaline degreasing and polishing pretreatment, ensures excellent corrosion resistance and coating adhesion for aluminum alloy plates while meeting environmental regulations.

[0054] Improved overall performance of the flame-retardant core layer: Through in-depth collaborative design of materials, processes, and equipment, especially core technologies such as segmented structured mixing, composite resin matrix, two-stage precision voltage stabilization, die temperature control and compensation, and stress-controlled cooling, the problems of simple blending of traditional flame retardant core layers, such as uneven dispersion, agglomeration, easy migration, and serious damage to mechanical properties and interfacial bonding, as well as poor processing stability, easy generation of bubbles, and warping, are solved.

[0055] Specially Designed for Interface Bonding: Unlike traditional single-layer adhesive films, which often fail to simultaneously match passivated aluminum sheet and highly filled flame-retardant core materials, the interface is easily weakened by additive migration. This functionalized three-layer composite adhesive film is co-extruded to form a metal interface bonding layer and a migration-resistant and stable middle bonding layer (bimodal LLDPE). This structure precisely adapts the characteristics of the upper and lower interfaces: the passivation-friendly layer strongly adheres to the aluminum alloy chromium-free passivation layer, the core-friendly layer is highly compatible with the flame-retardant core layer, and the middle layer provides bulk strength and effectively blocks the migration of the core layer additives to the aluminum sheet interface, achieving exceptionally strong and durable interlayer adhesion.

[0056] Flexible epoxy interface transition layer: A flexible epoxy interface bonding transition layer composed of bisphenol A epoxy resin + flexible long-chain epoxy addition modified polyamide is introduced between the chromium-free passivated aluminum plate and the decorative layer to effectively absorb and buffer stress, fundamentally preventing the decorative layer from cracking and peeling.

[0057] The protective performance of the back panel is significantly enhanced: Different from the traditional approach that only focuses on anti-corrosion, a special impact-resistant epoxy primer is applied to the lower surface of the chromium-free passivated back aluminum panel to form an impact-resistant epoxy primer protective layer, which improves the back panel's resistance to mechanical damage and corrosion resistance, reduces paint damage caused by carelessness during installation, and reduces the possibility of later corrosion.

[0058] PVDF protective layer with excellent comprehensive performance: Under the premise of ensuring environmental protection and safety, PVDF (F201) / acrylic resin (BN44) is used, and specific surface-modified nano-fillers and compounded light stabilizers are added. Through two coating-pre-curing and mirror roller calendering-main curing-cooling processes, the surface is given weather resistance, anti-fouling, wear resistance and mirror finish effects.

[0059] In summary, the present invention provides a comprehensive performance solution for the production of aluminum-plastic composite panels for interior decoration in terms of environmental protection, flame retardancy, mechanical properties, interface bonding reliability, etc. through a matching material system design and an innovative manufacturing process. DETAILED DESCRIPTION

[0060] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0061] Example 1

[0062] A wood-grain aluminum-plastic composite panel for interior decoration comprises a chrome-free passivated aluminum alloy plate, wherein the lower surface of the chrome-free passivated aluminum alloy plate is provided with an impact-resistant epoxy primer protective layer; the upper surface of the chrome-free passivated aluminum alloy plate is connected to the lower surface of an LDPE flame-retardant core layer via a lower adhesive film; the upper surface of the LDPE flame-retardant core layer is connected to the lower surface of the chrome-free passivated surface aluminum alloy plate via an upper adhesive film; both the lower adhesive film and the upper adhesive film are composite adhesive films, comprising a metal interface adhesive layer, an anti-migration stable intermediate adhesive layer, and a core material interface flame-retardant adhesive layer; the upper surface of the chrome-free passivated surface aluminum alloy plate is laminated in sequence from bottom to top with: a flexible epoxy interface bonding transition layer, a wood-grain pattern decorative layer, and a PVDF protective layer.

[0063] Example 2

[0064] A method for preparing an aluminum-plastic composite panel for interior decoration, used to prepare the aluminum-plastic composite panel in Example 1, specifically comprising the following steps:

[0065] S1 chromium-free passivation treatment: The back aluminum alloy plate and the front aluminum alloy plate are subjected to chromium-free passivation treatment respectively to obtain a chromium-free passivated back aluminum alloy plate and a chromium-free passivated front aluminum alloy plate; both the back aluminum alloy plate and the front aluminum alloy plate are 3003 aluminum alloy plates; the chromium-free passivation treatment includes ultrasonic weak alkaline degreasing, the first countercurrent water washing, polishing, the second countercurrent water washing, immersion passivation, low-conductivity water washing and drying;

[0066] Process optimization plan for weak alkaline degreasing cleaning solution for 3003 aluminum alloy: In ultrasonic weak alkaline degreasing and oil removal, the degreasing solution includes: 15-20g / L Texent610A surfactant, 8-10g / L AEO-9 surfactant, 6.0-7.0g / L sodium gluconate, 6.0-7.0g / L sodium silicate, 9-11g / L sodium carbonate and deionized water; sodium hydroxide is used as the pH value regulator; the pH value of the degreasing solution is 9.0-10.0. Control method: automatic dripping of NaOH, real-time monitoring and feedback. Temperature: 50–60℃; Ultrasonic parameters: Frequency: 40±2kHz (optimal cavitation intensity) Power density: ≥0.5W / cm 2 (To ensure micro-pore cleaning) Time: 3–5 min; Water quality requirements: Countercurrent water washing: conductivity ≤ 50 μS / cm;

[0067] In the light emitting process, Deoxidizer 150-40 light emitting agent is used;

[0068] A comprehensive optimization solution based on the Alodine 4830 / 4831 chromium-free passivation system: In a 1000L bath, add 6.5L of Alodine 4830, 12L of Alodine 4831, 0.5kg of citric acid, 0.35kg of succinic acid, and 0.85kg of potassium fluozirconate. This solution specifically addresses the manganese segregation problem in 3003 aluminum alloy while maintaining the environmental friendliness and process simplicity inherent in the Alodine system.

[0069] S2 Primer Coating: Coat the lower surface of the chrome-free passivated aluminum alloy plate with an impact-resistant and corrosion-resistant epoxy resin paint as a primer protective layer to obtain a pre-laminated back aluminum alloy plate; DreamCover221 aluminum alloy special paint is used;

[0070] S3: preparing a functional combination coating: sequentially preparing a flexible epoxy interface bonding transition layer, a patterned decorative layer, and a PVDF protective layer on the upper surface of the chromium-free passivated aluminum alloy plate to obtain a pre-composite aluminum alloy plate;

[0071] Flexible epoxy interface bonding transition layer: using bisphenol A epoxy resin and Versamid TM 115 modified curing agent; during the coating process, a precision roller coater (roller gap accuracy ±1μm) is used to apply a single coat on the surface of the chromium-free passivated aluminum alloy plate. After coating, it is leveled for 5 minutes (ambient temperature) and then cured.

[0072] Wood grain pattern decoration layer: The pattern decoration layer is prepared by vacuum thermal transfer process. The specific process is as follows: Pretreatment: After the epoxy flexible interface and anti-corrosion primer layer are subjected to electrostatic dust removal treatment; Transfer film preparation: A silicone release layer, a pattern decoration layer and an epoxy modified polyurethane hot melt adhesive are sequentially formed on the PET base film to form a transfer film; Hot press transfer: Heat to a preset temperature, apply a pressure of 0.5-1.5MPa, and maintain the temperature and pressure for 30-120 seconds; Release separation: After cooling, release the vacuum and peel off the release film;

[0073] PVDF protective layer: process flow: `batch → pre-dispersion → grinding → paint mixing → filtration → double-pass coating → pre-curing → mirror roller calendering → main curing → cooling`, the resin raw materials are F201 PVDF resin and BN44 acrylic resin, according to the weight ratio of 7:3; the main added auxiliary agents: 0.35% polydimethylsiloxane-b-polyoxyethylene; 0.6% hexamethyldisilazane surface modified fumed nano-silica; 0.5% isopropyl tris (dioctyl pyrophosphate acyloxy) titanate surface modified potassium titanate crystal; 0.4% γ-(2,3-epoxypropyl)-propyltrimethoxysilane surface modified γ-phase nano-alumina; 0.3% compound light stabilizer: hindered amine light stabilizer model is 111, triazine light stabilizer model is 1577, by weight ratio, hindered amine light stabilizer: triazine light stabilizer is 1:3; 0.12% polyacrylate leveling agent; mirror roller calendering: eliminates orange peel / pinholes, makes the surface extremely smooth, improves gloss consistency and enhances surface density.

[0074] S4 Preparation of flame retardant core layer: raw material pretreatment, segmented feeding and mixing, filtration, melt gear pump pressure stabilization, sheet extrusion, roller shaping and cooling operations are carried out in sequence to prepare the flame retardant core layer;

[0075] In the segmented feeding and mixing, the following settings are made: Section 1: preliminary melting section: a deep groove thread device is used for conveying; LDPE, mixed resin masterbatch, calcium stearate, EBS, and compound antioxidant are added through the main feeding port, partially melted by temperature control, and a viscoelastic continuous phase containing a solid particle carrier is formed; the resin raw materials used in the mixed resin masterbatch include LDPE, ionic ethylene-methacrylic acid copolymer resin, EVA, and LDPE-g-MAH, which are prepared by a co-blending extrusion process; the compound antioxidant includes hindered phenol antioxidants and phosphite antioxidants; Section 2: strong shear melting and separation Bulk section: Add surface-modified flame-retardant fillers, including surface-modified magnesium hydroxide, surface-modified aluminum hydroxide, and surface-modified magnesium-aluminum layered double hydroxide; Section three: Reverse thread devolatilization section: Inject molten oxidized polyethylene wax at the beginning of the reverse thread devolatilization section; configure a two-stage vacuum system and reverse thread elements; form a melt reflow zone through the reverse thread elements; Station four: Weak kneading and mixing section: Add surface-modified APP / MCA compound flame retardant additives and surface-modified zinc borate; Section five: Low shear homogenization section: Add molten PTFE and surface-modified short glass fibers;

[0076] According to the weight ratio, LDPE: mixed masterbatch: calcium stearate: EBS: compound antioxidant: surface-modified magnesium hydroxide: surface-modified aluminum hydroxide: surface-modified magnesium-aluminum layered double hydroxide: oxidized polyethylene wax: surface-modified APP / MCA compound flame retardant additive: surface-modified zinc borate: PTFE: surface-modified short glass fiber is 58:19:0.25:0.2:0.4:29:17:6:0.5:12:5:1:2;

[0077] In the mixed resin masterbatch, the weight ratio of LDPE:ionic ethylene-methacrylic acid copolymer resin:EVA:LDPE-g-MAH is 30:18:35:19, and the ionic ethylene-methacrylic acid copolymer resin is Surlyn 1855 resin;

[0078] The surface-modified flame-retardant filler is specifically surface-modified using a titanate coupling agent LK-101; the surface-modified APP / MCA compound flame-retardant additive is specifically an APP / MCA compound flame-retardant additive surface-modified with γ-methacryloxypropyltrimethoxysilane, with the weight ratio of APP:MCA being 3:1; the surface-modified zinc borate is specifically zinc borate surface-modified with a DL-411 aluminate coupling agent; and the surface-modified short glass fiber is specifically a short glass fiber surface-modified with γ-methacryloxypropyltrimethoxysilane.

[0079] In the deep-groove thread device, the screw groove depth-to-width ratio is ≥1.5, achieving gentle conveying; in the strong shear dispersion section, a 45° staggered angle kneading block element is configured; in the weak kneading and mixing section of station four, a neutral diamond-shaped kneading block element is used; in the low shear homogenization section of station five, a shallow-groove thin-walled screw element is configured, and the screw groove depth-to-width ratio is ≤0.8.

[0080] During the preparation of the flame-retardant core layer, the following are also set: in filtration, a double-column screen-changing filter device is used; in the melt gear pump pressure stabilization, a double-stage pressure stabilization technology is used, the main pump pressure stabilization: a high-precision involute gear pump is used, the outlet pressure fluctuation is ≤±0.3%, ensuring the stability of the melt flow; pulsation damper: a resonant pulsation damper is added to the gear pump outlet, and the pressure fluctuation is monitored in real time by a piezoelectric ceramic sensor, and the gear speed is adjusted by feedback; temperature control optimization: the gear pump adopts zoned temperature control, and the contact surface between the pump body and the melt is sprayed with a nano-zirconia thermal insulation coating; in extrusion molding, The die head features a coat-hanger-shaped flow channel structure, with the inner wall mirror-polished and coated with a corrosion-resistant alloy. The interior of the die head is divided into the following sections along the melt flow direction: a tapered diffusion zone, where the flow channel cross-section gradually expands to accommodate the melt from the melt gear pump; a flow distribution zone, where an adjustable flow block with a hyperbolic profile is built in; a steady flow convergence zone, where the flow channel cross-section gradually contracts and the surface is coated with a thermal insulation coating; and a die lip zone, where the die lip outlet is connected to a thickness pre-compensation device, allowing the discharge gap to be adjusted online. The die lip zone also features three independent temperature control sections, ensuring that the temperature on both sides is 2-5°C higher than that in the center to suppress edge shrinkage.

[0081] S5 Preparation of composite adhesive film: The composite adhesive film is prepared using a three-layer co-extrusion process; the resin raw materials for the metal interface adhesive layer include MAH-g-PE, EVA, and LDPE; the resin raw material for the anti-migration stable intermediate adhesive layer is bimodal LLDPE, and the anti-migration agent is polydopamine-coated nano-silica; the resin raw materials for the core material interface flame-retardant adhesive layer include mLLDPE, LDPE-g-MAH, and EVA, with surface-modified magnesium hydroxide added as a flame retardant additive;

[0082] In the metal interface bonding layer, the resins used are MAH-g-PE:EVA:LDPE in a weight ratio of 55:24:21. The middle layer uses bimodal LLDPE, and the anti-migration agent is polydopamine-coated nano-silica. In the core material interface flame-retardant bonding layer, the resins used are mLLDPE:LDPE-g-MAH:EVA:surface-modified magnesium hydroxide in a weight ratio of 35:30:35:8.

[0083] S6 pre-lamination: after surface treatment of the flame retardant core layer, a composite adhesive film is laminated on the upper and lower surfaces of the flame retardant core layer to obtain a pre-laminated flame retardant core layer;

[0084] S7 hot pressing lamination: The pre-laminated back aluminum alloy plate, pre-laminated flame-retardant core layer, and pre-laminated face aluminum alloy plate are stacked and assembled in order from bottom to top, and then subjected to staged gradient hot pressing lamination, edge sealing, and packaging operations to obtain an aluminum-plastic composite panel; the outer surface of the aluminum-plastic composite panel is covered with a peelable protective film; the peelable protective film is specifically a protective film made of BOPET;

[0085] The staged gradient hot pressing composite includes a preheating stage of exhaust and low-temperature initial bonding, a main composite stage of gradient heating and dynamic pressurization, a cooling stage of stress relaxation and gradient slow cooling, and a constant pressure aging curing stage.

[0086] In the preheating stage of exhaust and low-temperature initial adhesion, a pulse pressurized vacuum pre-pressurization exhaust method is used, and low-frequency mechanical vibration is applied simultaneously to assist exhaust and improve initial adhesion strength: pressure: 0.8-1.0MPa (pulse type: pressurization 5s / depressurization 2s) vacuum degree: ≤50Pa, vibration: 5Hz continuous low-frequency vibration, main compound stage: gradient heating dynamic pressurization: parameter setting: temperature gradient: 100℃→150℃→190℃ (each section is kept warm for 10min) pressure gradient: 2.0MPa at 100℃; ( Stable interlayer contact); 8.0MPa at 150℃ (activate EVA flow); 15.0MPa at 190℃ (complete melt infiltration) Cooling stage: stress relaxation and gradient slow cooling: parameter settings: cooling rate: 2-3℃ / min (190℃→80℃); holding pressure: 10.0MPa→5.0MPa (decreasing with temperature); relaxation time: constant temperature and pressure at 80℃ for 10-15min; aging curing stage: constant pressure at room temperature; parameter settings: pressure 0.5MPa, temperature 25℃.

[0087] Performance test: Take a number of aluminum-plastic composite panels in Example 1 for testing, and the specific test results are as follows:

[0088] As shown in Table 1:

[0089]

[0090]

[0091]

[0092]

[0093]

[0094] Table 1 Flame retardant performance test, the specific results are shown in Table 2:

[0095]

[0096]

[0097] Table 2

[0098] Comparing the test report data with the national standards, the test results of the following items are significantly better than the national standards, reflecting the outstanding advantages of product performance:

[0099] Material strength: The structure is more solid and durable: The national standard requirement for aluminum thickness is ≥0.20mm (thickness deviation ≤0.02mm). The actual measured results show that both the front aluminum and the back aluminum are 0.28mm (the deviation is only -0.01mm to 0mm). Advantages: The thickness of the aluminum layer is 40% thicker than the minimum requirement of the national standard, and the processing precision is extremely high (the deviation is close to 0), which greatly improves the impact resistance and service life of the plate.

[0100] Surface performance: Outstanding anti-fouling and protective capabilities: The national standard requirement for stain resistance is: stain residue ≤3%; actual measurement result: 1.1%; Advantage: The anti-fouling ability is improved by 63.3% compared with the national standard, making daily cleaning easier.

[0101] Coating thickness (minimum): National standard requirement: ≥23μm; measured result: 25μm; Advantage: The key protective layer is 8.7% thicker than the national standard, providing a stronger foundation for wear resistance and corrosion resistance;

[0102] Environmental Safety: Hazardous Substances "Not Detected": National standards for hazardous substances in the coating (9 items, including cadmium, mercury, and lead) require ≤0.1%; actual measurements show no detection (below the instrument detection limit). Hazardous substances in the core material (hexabromocyclododecane): National standards require no detection; actual measurements show no detection. Advantage: Actual hazardous substance content is "zero detection," far exceeding national standard thresholds for environmental safety.

[0103] Gloss deviation: measured 1.1 (national standard ≤ 7), aging resistance gloss loss rate: measured level 1 (national standard ≤ level 2), UV resistance improved by one level.

[0104] The specific embodiments described herein are merely illustrative of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments without departing from the spirit of the present invention or exceeding the scope thereof. While the present invention has been described and illustrated in detail in the foregoing description, such illustration and description are to be considered illustrative and exemplary rather than restrictive.

Claims

1. An aluminum-plastic composite panel for interior decoration, characterized in that: It includes a chrome-free passivated back aluminum alloy plate, the lower surface of which is provided with an impact-resistant epoxy primer protective layer; the upper surface of the chrome-free passivated back aluminum alloy plate is connected to the lower surface of the LDPE flame-retardant core layer through a lower adhesive film; the upper surface of the LDPE flame-retardant core layer is connected to the lower surface of the chrome-free passivated face aluminum alloy plate through an upper adhesive film; both the lower adhesive film and the upper adhesive film are composite adhesive films, and the composite adhesive film has a three-layer structure, including a metal interface adhesive layer, an anti-migration stable intermediate adhesive layer and a core material interface flame-retardant adhesive layer; the upper surface of the chrome-free passivated face aluminum alloy plate is stacked in sequence from bottom to top: a flexible epoxy interface bonding transition layer, a pattern decorative layer and a PVDF protective layer.

2. A method for preparing an aluminum-plastic composite panel for interior decoration, for preparing the aluminum-plastic composite panel for interior decoration as claimed in claim 1, characterized in that: The specific steps include: S1 chromium-free passivation treatment: The back aluminum alloy plate and the front aluminum alloy plate are subjected to chromium-free passivation treatment respectively to obtain a chromium-free passivated back aluminum alloy plate and a chromium-free passivated front aluminum alloy plate; both the back aluminum alloy plate and the front aluminum alloy plate are 3003 aluminum alloy plates; the chromium-free passivation treatment includes ultrasonic weak alkaline degreasing and degreasing, the first countercurrent water washing, polishing, the second countercurrent water washing, zirconium-based passivation, low-conductivity water washing and drying steps; S2 primer coating: coating the lower surface of the chromium-free passivated back aluminum alloy plate with an impact-resistant epoxy resin paint as an impact-resistant epoxy primer protective layer to obtain a pre-composite back aluminum alloy plate; S3: preparing a functional coating: sequentially preparing a flexible epoxy interface bonding transition layer, a patterned decorative layer, and a PVDF protective layer on the upper surface of the chromium-free passivated aluminum alloy plate to obtain a pre-composite aluminum alloy plate; When preparing the flexible epoxy interface bonding transition layer, bisphenol A epoxy resin and flexible long-chain epoxy addition modified polyamide curing agent are used; When preparing the pattern decoration layer, a vacuum thermal transfer process is adopted. The thermal transfer film structure used is, from top to bottom, a PET base film, a silicone release layer, a pattern printing layer, and an epoxy-modified polyurethane hot-melt adhesive layer. The PVDF protective layer is prepared using a two-layer coating-precuring and mirror roller calendering-main curing-cooling process. The requirements are as follows: PVDF resin: F201 type; thermoplastic acrylic resin: molecular weight 70,000-90,000 g / mole; acid value <2 mgKOH / g; chromaticity (Fe-Co) ≤ 1; functional additives: polydimethylsiloxane-b-polyethylene oxide, surface-modified fumed nanosilica, surface-modified potassium titanate whiskers, surface-modified γ-phase nanoalumina, hindered amine and triazine compound light stabilizers, and acrylate or polyacrylate leveling agents. S4 preparation of LDPE flame retardant core layer: raw material pretreatment, segmented feeding and mixing, filtration, melt gear pump pressure stabilization, sheet extrusion, roller shaping and cooling operations are carried out in sequence to prepare the LDPE flame retardant core layer; In the segmented feeding and mixing, the following settings are made: Section 1: Initial melting section: A deep groove thread device is used for conveying; LDPE, mixed resin masterbatch, calcium stearate, EBS, and compound antioxidant are added through the main feeding port, partially melted by temperature control, and a viscoelastic continuous phase containing a solid particle carrier is formed; the resin used in the mixed resin masterbatch includes LDPE, ionic ethylene-methacrylic acid copolymer resin, EVA, and LDPE-g-MAH, which are prepared by a co-blending extrusion process; the compound antioxidant includes hindered phenol antioxidants and phosphite antioxidants; Section 2: Strong shear melt dispersion section: Add surface-modified flame-retardant fillers, including magnesium hydroxide, aluminum hydroxide, and magnesium-aluminum layered double hydroxide; Section 3: Reverse thread devolatilization section: Inject molten oxidized polyethylene wax at the beginning of the reverse thread devolatilization section; Configure a two-stage vacuum system and reverse thread elements; Form a melt reflow zone through the reverse thread elements; Section 4: Weak kneading and mixing section: Add surface-modified APP / MCA compound flame retardant additives and surface-modified zinc borate; Section 5: Low shear homogenization section: Add molten PTFE and surface-modified short glass fibers; S5 Preparation of composite adhesive film: The composite adhesive film is prepared using a three-layer co-extrusion process; the resins used in the metal interface adhesive layer include MAH-g-PE, EVA, and LDPE; the resin used in the anti-migration stabilization intermediate adhesive layer is bimodal LLDPE, and the anti-migration agent is polydopamine-coated nano-silica; the resins used in the core material interface flame-retardant adhesive layer include mLLDPE, LDPE-g-MAH, and EVA, with surface-modified magnesium hydroxide added as a flame retardant additive; S6 pre-lamination: After surface treatment of the flame retardant core layer, a composite adhesive film is laminated on the upper and lower surfaces of the flame retardant core layer to obtain a pre-laminated flame retardant core layer; S7 hot pressing composite: The pre-composite back aluminum alloy plate, pre-composite flame-retardant core layer and pre-composite face aluminum alloy plate are stacked and assembled in order from bottom to top, and then hot pressing composite, edge sealing and packaging operations are carried out in sequence to obtain the aluminum-plastic composite panel; the staged hot pressing composite includes a preheating stage of exhaust and low-temperature initial bonding, a main composite stage of dynamic heating and pressurization, a cooling stage of stress relaxation and slow cooling, and a constant pressure aging curing stage.

3. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S1, in ultrasonic weak alkaline degreasing and oil removal, the raw materials used include Texent610A surfactant, AEO-9 surfactant, sodium gluconate, sodium silicate, sodium hydroxide and sodium carbonate; In the light emitting process, Deoxidizer 150-40 light emitting agent is used; Zirconium-based passivation: passivator: Alodine4830 / 4831 passivator; auxiliary passivators: succinic acid, citric acid and potassium fluorozirconate.

4. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S2, the epoxy resin paint with impact resistance and corrosion resistance is specifically DreamCover221 aluminum alloy special paint.

5. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S3, the flexible long-chain epoxy addition modified polyamide is specifically Versamid 115 modified polyamide.

6. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S3, the surface-modified fumed nano-silica is specifically hexamethyldisilazane surface-modified fumed nano-silica; the surface-modified potassium titanate whiskers are specifically isopropyl tris(dioctyl pyrophosphate acyloxy) titanate surface-modified potassium titanate crystals; the surface-modified γ-phase nano-alumina is specifically γ-(2,3-epoxypropyl)-propyltrimethoxysilane surface-modified γ-phase nano-alumina; the hindered amine light stabilizer model is 111, triazine light stabilizer model is 1577, according to the weight ratio, the hindered amine light stabilizer: triazine light stabilizer is 1:2.5-3.

7. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S4, according to the weight ratio, LDPE: mixed masterbatch: calcium stearate: EBS: compound antioxidant: surface-modified magnesium hydroxide: surface-modified aluminum hydroxide: surface-modified magnesium-aluminum layered double hydroxide: oxidized polyethylene wax: surface-modified APP / MCA compound flame retardant additive: surface-modified zinc borate: PTFE: surface-modified short glass fiber is: 55-60:17-23:0.2-0.25:0.2-0.3:0.4-0.5:25-30:15-20:5-8:0.45-0.6:10-12:4-5:0.8-1.2:2-3； In the mixed resin masterbatch, the weight ratio of LDPE:ionic ethylene-methacrylic acid copolymer resin:EVA:LDPE-g-MAH is 30-32:17.5-18:32-35:17.5-20, and the ionic ethylene-methacrylic acid copolymer resin is surlyn1855 type resin; In the compound antioxidant, the mass ratio of hindered phenol antioxidant 1010 to phosphite antioxidant 168 is 1:1-1.2; In the surface-modified flame-retardant filler, at least one of γ-methacryloxypropyltrimethoxysilane and titanate coupling agent LK-101 is specifically used for surface modification, and in the magnesium-aluminum layered double hydroxide, the magnesium content: aluminum content is 2-3:1; The surface-modified APP / MCA compound flame retardant additive is specifically a surface-modified APP / MCA compound flame retardant additive of γ-methacryloxypropyltrimethoxysilane, wherein the weight ratio of APP:MCA is 2.5-3:1; The surface-modified zinc borate is specifically zinc borate surface-modified with DL-411 aluminate coupling agent; The surface-modified short glass fiber is specifically a short glass fiber surface-modified with γ-methacryloxypropyltrimethoxysilane; In the deep-groove thread device, the screw groove depth-to-width ratio is ≥1.5, achieving gentle conveying; in the strong shear dispersion section, a 45° staggered angle kneading block element is configured; in the weak kneading and mixing section of station four, a neutral diamond-shaped kneading block element is used; in the low shear homogenization section of station five, a shallow-groove thin-walled screw element is configured, and the screw groove depth-to-width ratio is ≤0.

8.

8. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S4, during the preparation of the LDPE flame-retardant core layer, the following settings are also made: in filtration, a double-column screen-changing filter device is used; in melt gear pump pressure stabilization, a two-stage pressure stabilization technology is used, main pump pressure stabilization: a high-precision involute gear pump is used, and the outlet pressure fluctuation is ≤±0.3% to ensure the stability of the melt flow; pulsation damper: a resonant pulsation damper is added to the gear pump outlet, and the pressure fluctuation is monitored in real time by a piezoelectric ceramic sensor, and the gear speed is adjusted by feedback; temperature control optimization: the gear pump adopts zoned temperature control, and the contact surface between the pump body and the melt is sprayed with a nano-zirconia thermal insulation coating; in extrusion molding, the die head adopts a hanger-type flow channel structure, and the inner wall of the flow channel is mirror-polished and coated with a corrosion-resistant alloy layer; the interior of the die head is divided into the following parts along the melt flow direction: a conical diffusion zone: the flow channel cross-section gradually expands to adapt to the melt of the melt gear pump; a flow resistance distribution zone: It has a built-in adjustable baffle with a double-curvature profile design; the steady flow bunching area has a gradually shrinking flow channel cross-section and a heat-insulating coating on the surface; the die lip area has a die lip outlet connection thickness pre-compensation device, and the discharge gap can be adjusted online; the three lateral temperature sections of the die lip area are independently regulated, so that the temperature on both sides is 2-5°C higher than that in the center area to suppress the edge shrinkage effect; in the roller shaping process, a three-roll calender is used, and a melt elastic pre-relaxation zone is added at the roller inlet to avoid warping caused by fiber orientation; in the cooling process, a contact-type gradient slow cooling section and a forced air cooling section are provided. In the contact-type gradient slow cooling section, a cooling roller device is used for cooling; in the forced air cooling section, a multi-bellows turbulent cooling system is used, and an asymmetric cooling strategy is adopted, with the lower layer wind pressure greater than the upper layer wind pressure, to compensate for the curvature deformation caused by the deadweight of the core layer, and annular gap air nozzles are added on both sides to suppress edge curling.

9. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S5, in the metal interface bonding layer, the resin used is MAH-g-PE:EVA:LDPE in a weight ratio of 50-55:20-25:20-25; in the core material interface flame retardant bonding layer, the resin used is mLLDPE:LDPE-g-MAH:EVA:surface-modified magnesium hydroxide in a weight ratio of 35-40:25-30:35-40:6-8.

10. The method for preparing the aluminum-plastic composite panel for interior decoration according to claim 2, wherein: In step S7, during the preheating stage of exhaust and low-temperature initial bonding, a pulse pressurized vacuum pre-compression exhaust method is adopted, and low-frequency mechanical vibration is applied synchronously to assist exhaust and improve initial bonding strength.

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