A metal can packaging material and a method for manufacturing the same

Abstract

The present application relates to the technical field of metal packaging container manufacturing, in particular to a metal can packaging material and a preparation method thereof. First, the metal substrate is subjected to double-side alkaline washing, pickling and chromium-free passivation pretreatment; then a nano-porous adhesive layer, an ion exchange corrosion-resistant layer and a hydrophobic protective layer are sequentially constructed on the inner wall surface to form a composite coating as the inner wall of the metal can; then the metal substrate is processed into a can body; finally, a decorative primer and a finishing varnish are coated on the outer wall of the can body. The method significantly enhances the adhesion of the coating during processing through the optimized multi-layer protection of the inner wall of the metal can body, achieves active corrosion prevention and safety barrier capability for the objects contained in the metal can body, and at the same time, the outer wall obtains good decorative and physical protection effects, thereby comprehensively improving the durability, safety and commodity value of the metal can.

Description

Technical Field

[0001] This invention relates to the field of metal packaging container manufacturing technology, specifically to a metal can packaging material and its preparation method. Background Technology

[0002] With the market's ever-increasing demands for food quality and the trend towards lightweight and sustainable packaging, existing coating technologies are facing increasingly stringent challenges. Currently, the industry mainstream still widely uses organic coating systems such as epoxy phenolic resins and epoxy-acrylic resins. These coatings primarily isolate the contents from the metal substrate through a physical barrier layer formed after curing, thereby preventing corrosion and metal ion migration to a certain extent and ensuring basic food safety. However, in large-scale production, long-term storage, and practical applications involving diverse contents, traditional coating technologies are gradually revealing their systemic technical bottlenecks and performance limitations.

[0003] Specifically, the protective mechanism of traditional coatings relies on the density of the cured film for passive barrier. When exposed to acidic beverages, salty foods, or contents rich in proteins and sulfur compounds, corrosive media such as hydrogen ions, chloride ions, and sulfide ions in the contents can easily penetrate the coating and reach the metal interface, causing chemical or electrochemical corrosion. This can ultimately lead to serious consequences such as can perforation and spoilage of the contents. Secondly, regarding the bonding between the coating and the substrate, existing processes mainly rely on the mechanical interlocking effect provided by the surface roughness of the substrate and the physical adsorption generated by polar functional groups. This bonding method can be maintained under static conditions, but it is relatively fragile under dynamic processing conditions such as can forming, welding, and sterilization, as well as under the stress of long-term use. Insufficient interfacial bonding can easily lead to coating peeling. In addition, traditional coatings are passive defense types with limited functions and lack active protection or self-repair capabilities. Once the coating suffers microscopic damage due to processing or transportation, corrosion will occur in a point-like manner and spread rapidly, while the coating itself does not have a mechanism to inhibit or repair the damage. Although the industry has explored the introduction of some new technologies to enhance functionality, these often affect the film formation continuity of the coating, food contact safety, or significantly increase process complexity and cost, making it difficult to achieve stable and large-scale application in the demanding food can sector.

[0004] In summary, these issues limit the application of metal cans in more demanding food contents and also affect their long-term storage safety and production yield. Therefore, there is an urgent need for a comprehensive innovative coating solution that integrates protection concepts, material systems, and manufacturing processes. The aim is to construct a multi-level, synergistic, composite protection system combining active and passive protection, thereby providing core technological support for the next generation of high-performance, high-safety, and high-reliability metal food can packaging. Summary of the Invention

[0005] In view of the problems existing in the above-mentioned background technology, the present invention proposes a method for preparing metal can packaging materials, including the following steps.

[0006] S1. After pretreatment of the metal substrate, rinse it quickly with deionized water, and then dry it thoroughly with hot air at 100-120℃ immediately.

[0007] S2. On the surface of the pretreated substrate, a nanoporous adhesive layer is formed on one side of the substrate through a coating and curing process on the inner wall of the tank.

[0008] S3. An ion-exchange anti-corrosion layer is formed on the nanoporous adhesive layer by deposition. After deposition, the metal substrate is gently rinsed with deionized water to remove loosely attached particles on the surface, and then dried at 80°C for 10 minutes.

[0009] S4. A hydrophobic protective layer is formed on the ion exchange anti-corrosion layer by high-voltage electrostatic spraying and curing.

[0010] S5. The metal substrate having the nanoporous adhesive layer, ion exchange anti-corrosion layer and hydrophobic protective layer on one side is processed into a metal tank as the inner wall.

[0011] S6. Apply an outer wall decorative protective layer to the outer surface of the metal tank.

[0012] Preferably, in step S1, the metal substrate is tinplate, and the pretreatment steps are as follows: the metal substrate is subjected to alkaline washing, acid washing, and passivation treatment in sequence. The passivation treatment is carried out using a chromium-free passivation solution. Alkaline washing mainly removes rolling oil and reduces residual organic matter from damaging the adhesion of the coating on the metal substrate. Acid washing is used to dissolve the surface oxide layer. Chromium-free passivation can form a nanoscale passivation film, which not only provides short-term rust prevention, but its porous structure also facilitates bonding with subsequent coatings. After pretreatment, the substrate must be temporarily stored in a dry environment to prevent the surface hydroxyl groups from deactivating due to combination with moisture.

[0013] Preferably, the steps of alkaline washing, acid washing and passivation treatment of the metal substrate are as follows: immerse the metal substrate in a sodium hydroxide aqueous solution with a temperature of 55-65℃ and a concentration of 45-55 g / L for 2-4 minutes; then spray or rinse the metal substrate with running water until the water film on the substrate surface is uniform, without water droplets, and the pH value of the outflowing water is close to neutral, at which point the pH is 6.6-7.0; next, immerse the water-washed metal substrate in a sulfuric acid aqueous solution with a temperature of 45-55℃ and a concentration of 140-160 g / L for 1.5-2.5 minutes; finally, immerse the metal substrate in a chromium-free passivation solution with a temperature of 20-40℃ for 60-90 seconds. The preparation process of the chromium-free passivation solution is as follows: mix 4 parts of γ-glycidyl etheroxypropyltrimethoxysilane with 16 parts of anhydrous ethanol and stir for 20 minutes. While stirring, slowly add it to 80 parts of deionized water with pH adjusted to 5.0. Continue stirring for 2 hours, then seal and let it stand at room temperature for 24 hours before use.

[0014] Preferably, in step S2, the coating and curing process involves hydrolyzing and condensing tetrabutyl orthosilicate and tetrabutyl titanate under acidic catalysis at pH 3.5-4.0, aging for 24 hours to form a stable composite sol, and then applying it to the highly active surface of the pretreated metal substrate using a dip-coating method at a uniform speed of 5 mm / s, followed by drying at 110-130°C for 20-40 minutes.

[0015] Preferably, in step S3, the deposition step involves immersing the metal substrate treated in step S2 as a cathode in an electrophoretic solution and electrophoretically depositing it at a constant voltage of 20V for 2 minutes. The electrophoretic solution is prepared by dispersing 5 wt% sodium-based montmorillonite and 1 wt% conductive polyaniline in the form of emerald green imine salt in deionized water and mixing thoroughly. The ion exchange properties of montmorillonite in this layer can actively adsorb corrosive agents such as Cl⁻, while polyaniline can undergo a reversible redox transition under the action of a corrosion micro-cell. The accompanying volume change and reaction products can partially compensate for and repair adjacent coating micro-defects, achieving a self-healing function.

[0016] Preferably, in step S4, the coating and curing step involves electrostatically spraying the modified acrylic resin onto the surface at an atomization pressure of 0.6 MPa and a spraying distance of 20 cm using high-voltage electrostatic spraying, followed by curing at 170-190°C for 25-35 minutes to form a hydrophobic protective layer. Based on hydroxyl acrylic resin, 2-5% of a fluorosilane coupling agent (such as tridecafluorooctyltriethoxysilane) and 3-8% of a nano-silica dispersion are slowly added to the resin under stirring. The mixture is then continuously stirred at 2000-3000 rpm for 30-60 minutes using a high-speed disperser to ensure uniform dispersion of the functional additives and the formation of a stable composite system. Finally, the uniformly mixed resin is allowed to stand at room temperature for 2-4 hours to mature, yielding a hydrophobic modified acrylic resin suitable for subsequent electrostatic spraying.

[0017] Preferably, in step S5, the tank body is processed by forming a tank body from a metal substrate using a three-piece tank forming machine, and the tank body weld is laser welded with a welding power of 1.8-2.2kW and a welding speed of 2.8-3.2m / min.

[0018] Preferably, in step S6, the outer surface is coated with an outer wall decorative protective layer by transporting the formed can in step S5 to the spraying line and fixing it on the rotating spraying bracket to ensure that the can rotate at a uniform speed, and then applying a decorative primer and a clear topcoat in sequence, and finally curing it at high temperature to form an outer wall decorative protective layer.

[0019] Preferably, after the decorative primer is sprayed, it is leveled and pre-cured at 120-140℃ for 2-4 minutes, and then a hydroxyl acrylic resin topcoat is sprayed. The high-temperature curing is to bake at 180-200℃ for 10-15 minutes.

[0020] Preferably, a metal can packaging material is prepared by a method for preparing metal can packaging materials.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1) The nanoporous adhesive layer, with its three-dimensional interconnected inorganic network structure and huge specific surface area, provides the entire coating with a strong mechanical anchoring force that surpasses traditional physical adsorption. It can effectively buffer the severe deformation and thermal stress generated in the tank during molding, welding and sterilization, fundamentally solving the industry pain point of easy peeling of the coating in the weld seam and deformation area, and ensuring the solidity of the coating system substrate.

[0022] 2) The middle ion exchange anti-corrosion layer creatively introduces montmorillonite / polyaniline intercalation composite material, which not only plays a physical barrier role, but also actively adsorbs and neutralizes corrosive ions such as Cl⁻ and SO4²⁻ that migrate from the contents through ion exchange characteristics, which greatly extends the anti-corrosion life in harsh contents environments such as acidic and high salt.

[0023] 3) The outermost hydrophobic protective layer is made of modified acrylic resin, which greatly reduces the wetting and penetration of liquid media on the tank wall from the source. Together with the middle layer, it forms a double line of defense. At the same time, by selecting food-safe raw materials, absolute safety is ensured and the risk of migration of harmful substances is eliminated.

[0024] This invention constructs a composite coating system on the inner wall, in conjunction with a decorative coating on the outer wall. The inner wall focuses on long-term corrosion protection and safety isolation, while the outer wall, through the application of a decorative primer and a high-performance clear varnish, focuses on meeting the aesthetic requirements of product display and the physical protection requirements such as wear resistance and scratch resistance needed for transportation and stacking. Both processes are completed on a continuous production line, achieving a balance between functional complementarity and manufacturing efficiency, and systematically solving the inherent defects of traditional food can inner wall coatings in terms of corrosion protection, adhesion, and safety. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of the present invention is for describing specific implementation schemes and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0026] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, can be implemented using any prior art methods, equipment, and materials similar to or equivalent to the methods, equipment, and materials in the embodiments of this invention. In the following embodiments, unless specific conditions are specified, conventional conditions or conditions recommended by the manufacturer are followed. All reagents used, unless otherwise specified, are conventional reagents used in the art, and all reagents or instruments used, unless otherwise specified by the manufacturer, are commercially available conventional products.

[0027] Example 1

[0028] A method for preparing a metal can packaging material includes the following steps:

[0029] S1. After pretreatment of the metal substrate by alkaline washing, acid washing and passivation, it is quickly rinsed with deionized water and then immediately dried thoroughly in hot air at 110℃. The steps of alkaline washing, acid washing and passivation are as follows: immerse the metal substrate in a sodium hydroxide aqueous solution with a temperature of 60℃ and a concentration of 50g / L for 3 minutes, then spray or immerse the metal substrate with running clean water until the water film on the substrate surface is uniform, no water droplets are attached, and the pH value of the outflowing water is close to neutral. Then immerse the washed metal substrate in a sulfuric acid aqueous solution with a temperature of 50℃ and a concentration of 150g / L for 2 minutes. Finally, immerse the metal substrate in a chromium-free passivation solution with a temperature of 30℃ for 75 seconds.

[0030] S2. On the surface of the pretreated metal substrate, tetraethyl orthosilicate and tetrabutyl titanate are hydrolyzed and condensed under acid catalysis on one side, and aged for 24 hours to form a stable composite sol. The sol is then coated on the highly active surface of the pretreated metal substrate by dip coating at a uniform speed of 5 mm / s, and then dried at 120°C for 30 minutes to form a nanoporous adhesive layer.

[0031] S3. On the nanoporous adhesive layer, the metal substrate treated in step S2 is immersed in the electrophoretic solution as the cathode and electrophoresed for 2 minutes at a constant voltage of 20V. The electrophoretic solution is prepared by dispersing 5wt% sodium montmorillonite and 1wt% conductive polyaniline in deionized water and stirring thoroughly. After deposition, the metal substrate is gently rinsed with deionized water to remove loosely attached particles on the surface and then dried at 80°C for 10 minutes.

[0032] S4. On the ion exchange anti-corrosion layer, the modified acrylic resin is sprayed onto the surface by high-pressure electrostatic spraying at an atomization pressure of 0.6MPa and a spraying distance of 20cm, and then cured at 180℃ for 30 minutes to form a hydrophobic protective layer.

[0033] S5. The metal substrate with one side having a nanoporous bonding layer, an ion exchange anti-corrosion layer and a hydrophobic protective layer is used as the inner wall to process into a metal tank. The tank is processed by processing the metal substrate into a tank using a three-piece tank forming machine. The tank weld is laser welded with a welding power of 2kW and a welding speed of 3m / min.

[0034] S6. The formed can in step S5 is transported to the spraying line and fixed on the rotating spraying bracket to ensure that the can rotate at a uniform speed. Then, the decorative primer is sprayed. After the decorative primer is sprayed, it is leveled and pre-cured at 130°C for 3 minutes. Then, the hydroxyl acrylic resin system topcoat is sprayed. Finally, it is baked at 190°C for 12 minutes for high-temperature curing to form the outer wall decorative protective layer.

[0035] Example 2

[0036] A method for preparing a metal can packaging material includes the following steps:

[0037] S1. After pretreatment of the metal substrate by alkaline washing, acid washing and passivation, it is quickly rinsed with deionized water and then immediately dried thoroughly under hot air at 100°C. The steps of alkaline washing, acid washing and passivation are as follows: immerse the metal substrate in a sodium hydroxide aqueous solution with a temperature of 55°C and a concentration of 45 g / L for 2 minutes, then spray or rinse the metal substrate with running clean water until the water film on the substrate surface is uniform, no water droplets are attached, and the pH value of the outflowing water is close to neutral. Then immerse the washed metal substrate in a sulfuric acid aqueous solution with a temperature of 45°C and a concentration of 140 g / L for 1.5 minutes. Finally, immerse the metal substrate in a chromium-free passivation solution with a temperature of 20°C for 60 seconds.

[0038] S2. On the surface of the pretreated metal substrate, tetraethyl orthosilicate and tetrabutyl titanate are hydrolyzed and condensed under acid catalysis on one side, and aged for 24 hours to form a stable composite sol. The sol is then coated on the highly active surface of the pretreated metal substrate by dip coating at a uniform speed of 5 mm / s, and then dried at 110°C for 20 minutes to form a nanoporous adhesive layer.

[0039] S3. On the nanoporous adhesive layer, the metal substrate treated in step S2 is immersed in the electrophoretic solution as the cathode and electrophoresed for 2 minutes at a constant voltage of 20V. The electrophoretic solution is prepared by dispersing 5wt% sodium montmorillonite and 1wt% conductive polyaniline in deionized water and stirring thoroughly. After deposition, the metal substrate is gently rinsed with deionized water to remove loosely attached particles on the surface and then dried at 80°C for 10 minutes.

[0040] S4. On the ion exchange anti-corrosion layer, the modified acrylic resin is sprayed onto the surface by high-pressure electrostatic spraying at an atomization pressure of 0.6MPa and a spraying distance of 20cm, and then cured at 170℃ for 25 minutes to form a hydrophobic protective layer.

[0041] S5. The metal substrate with one side having a nanoporous bonding layer, an ion exchange anti-corrosion layer and a hydrophobic protective layer is used as the inner wall to process into a metal tank. The tank is processed by processing the metal substrate into a tank using a three-piece tank forming machine. The tank welds are laser welded with a welding power of 1.8kW and a welding speed of 2.8m / min.

[0042] S6. The formed can in step S5 is transported to the spraying line and fixed on the rotating spraying bracket to ensure that the can rotate at a uniform speed. Then, the decorative primer is sprayed. After the decorative primer is sprayed, it is leveled and pre-cured at 120°C for 2 minutes. Then, the hydroxyl acrylic resin system topcoat is sprayed. Finally, it is baked at 180°C for 10 minutes for high-temperature curing to form the outer wall decorative protective layer.

[0043] Example 3

[0044] A method for preparing a metal can packaging material includes the following steps:

[0045] S1. After pretreatment of the metal substrate by alkaline washing, acid washing and passivation, it is quickly rinsed with deionized water and then immediately dried thoroughly in hot air at 120°C. The steps of alkaline washing, acid washing and passivation are as follows: the metal substrate is immersed in a sodium hydroxide aqueous solution with a temperature of 65°C and a concentration of 55 g / L for 4 minutes, and then the metal substrate is sprayed or rinsed with running clean water until the water film on the substrate surface is uniform, no water droplets are attached, and the pH value of the outflowing water is close to neutral. Then, the washed metal substrate is immersed in a sulfuric acid aqueous solution with a temperature of 55°C and a concentration of 160 g / L for 2.5 minutes. Finally, the metal substrate is immersed in a chromium-free passivation solution with a temperature of 40°C for 90 seconds.

[0046] S2. On the surface of the pretreated metal substrate, tetraethyl orthosilicate and tetrabutyl titanate are hydrolyzed and condensed under acid catalysis on one side, and aged for 24 hours to form a stable composite sol. The sol is then coated on the highly active surface of the pretreated metal substrate by dip coating at a uniform speed of 5 mm / s, and then dried at 130°C for 40 minutes to form a nanoporous adhesive layer.

[0047] S3. On the nanoporous adhesive layer, the metal substrate treated in step S2 is immersed in the electrophoretic solution as the cathode and electrophoresed for 2 minutes at a constant voltage of 20V. The electrophoretic solution is prepared by dispersing 5wt% sodium montmorillonite and 1wt% conductive polyaniline in deionized water and stirring thoroughly. After deposition, the metal substrate is gently rinsed with deionized water to remove loosely attached particles on the surface and then dried at 80°C for 10 minutes.

[0048] S4. On the ion exchange anti-corrosion layer, the modified acrylic resin is sprayed onto the surface by high-pressure electrostatic spraying at an atomization pressure of 0.6MPa and a spraying distance of 20cm, and then cured at 190℃ for 35 minutes to form a hydrophobic protective layer.

[0049] S5. The metal substrate with one side having a nanoporous bonding layer, an ion exchange anti-corrosion layer and a hydrophobic protective layer is used as the inner wall to process into a metal tank. The tank is processed by processing the metal substrate into a tank using a three-piece tank forming machine. The tank welds are laser welded with a welding power of 2.2kW and a welding speed of 3.2m / min.

[0050] S6. The formed tank in step S5 is transported to the spraying line and fixed on the rotating spraying bracket to ensure that the tank can rotate at a uniform speed. Then, the decorative primer is sprayed. After the decorative primer is sprayed, it is leveled and pre-cured at 140°C for 4 minutes. Then, the hydroxyl acrylic resin system topcoat is sprayed. Finally, it is baked at 200°C for 15 minutes for high-temperature curing to form the outer wall decorative protective layer.

[0051] Example 4

[0052] A method for preparing a metal can packaging material includes the following steps:

[0053] S1. After pretreatment of the metal substrate by alkaline washing, acid washing and passivation, it is quickly rinsed with deionized water and then immediately dried thoroughly in hot air at 110℃. The steps of alkaline washing, acid washing and passivation are as follows: immerse the metal substrate in a sodium hydroxide aqueous solution with a temperature of 60℃ and a concentration of 45g / L for 4 minutes, then spray or rinse the metal substrate with running clean water until the water film on the substrate surface is uniform, no water droplets are attached, and the pH value of the outflowing water is close to neutral. Then immerse the washed metal substrate in a sulfuric acid aqueous solution with a temperature of 55℃ and a concentration of 145g / L for 2 minutes. Finally, immerse the metal substrate in a chromium-free passivation solution with a temperature of 25℃ for 70 seconds.

[0054] S2. On the surface of the pretreated metal substrate, tetraethyl orthosilicate and tetrabutyl titanate are hydrolyzed and condensed under acid catalysis on one side, and aged for 24 hours to form a stable composite sol. The sol is then coated on the highly active surface of the pretreated metal substrate by dip coating at a uniform speed of 5 mm / s, and then dried at 125°C for 35 minutes to form a nanoporous adhesive layer.

[0055] S3. On the nanoporous adhesive layer, the metal substrate treated in step S2 is immersed in the electrophoretic solution as the cathode and electrophoresed for 2 minutes at a constant voltage of 20V. The electrophoretic solution is prepared by dispersing 5wt% sodium montmorillonite and 1wt% conductive polyaniline in deionized water and stirring thoroughly. After deposition, the metal substrate is gently rinsed with deionized water to remove loosely attached particles on the surface and then dried at 80°C for 10 minutes.

[0056] S4. On the ion exchange anti-corrosion layer, the modified acrylic resin is sprayed onto the surface by high-pressure electrostatic spraying at an atomization pressure of 0.6MPa and a spraying distance of 20cm, and then cured at 175℃ for 30 minutes to form a hydrophobic protective layer.

[0057] S5. The metal substrate having the nanoporous bonding layer, ion exchange anti-corrosion layer and hydrophobic protective layer on one side is used as the inner wall to process into a metal tank. The tank is processed by processing the metal substrate into a tank using a three-piece tank forming machine. The tank weld is laser welded with a welding power of 1.9kW and a welding speed of 2.9m / min.

[0058] S6. The formed can in step S5 is transported to the spraying line and fixed on the rotating spraying bracket to ensure that the can rotate at a uniform speed. Then, the decorative primer is sprayed. After the decorative primer is sprayed, it is leveled and pre-cured at 125°C for 3 minutes. Then, the hydroxyl acrylic resin system topcoat is sprayed. Finally, it is baked at 195°C for 13 minutes for high-temperature curing to form the outer wall decorative protective layer.

[0059] Comparative Example 1

[0060] The chromium-free passivation solution was replaced with a traditional passivation solution containing hexavalent chromium, and a solution containing 5 g / L Na2Cr2O7 was used to treat the pickled metal substrate at 35°C for 90 seconds. The rest of the preparation process and parameters were completely consistent with those in Example 1.

[0061] Comparative Example 2

[0062] In Comparative Example 2, the preparation of the nanoporous adhesive layer in step S2 of Example 1 was omitted. After the metal substrate was pretreated by alkaline washing, acid washing and chromium-free passivation, step S3 was directly performed on the surface of the metal substrate to form an ion exchange anti-corrosion layer. The rest of the preparation process and parameters were completely consistent with those in Example 1.

[0063] Comparative Example 3

[0064] In Comparative Example 3, the preparation process of the ion exchange anti-corrosion layer in step S3 of Example 1 was omitted. After completing step S2 and drying, the operation of step S4 was performed directly on its surface. The remaining preparation process and parameters were completely consistent with those in Example 1.

[0065] The products prepared in Example 1 and Comparative Examples 1-3 were tested. The results showed that: Example 1, due to its chromium-free passivation process, had no detectable chromium content in its passivation film, fully complying with food contact material regulations; while Comparative Example 1 used a traditional chromium-containing passivation solution with a chromium content exceeding 200 μg / dm², posing a clear safety hazard. Furthermore, regarding the interfacial adhesion that determines coating durability, Example 1 exhibited superior performance, with a weld coating peel strength of no less than 8.0 MPa; while Comparative Example 2, lacking a nanoporous bonding layer, saw this strength plummet to below 3.0 MPa, confirming that this layer is key to solving the coating peeling problem during processing. In addition, regarding corrosion resistance, Example 1's salt spray test time exceeded 800 hours, demonstrating exceptional corrosion resistance life; while Comparative Example 3, lacking an ion exchange layer, had a salt spray time of less than 300 hours, significantly reducing its active corrosion resistance, proving that the ion exchange anti-corrosion layer is the core for achieving long-term corrosion protection.

[0066] In summary, this invention achieves synergistic breakthroughs in environmental friendliness, adhesion, corrosion resistance, and processing adaptability through innovation in material systems and processes, providing a high-performance, high-safety, and high-reliability comprehensive solution for metal can packaging, demonstrating significant technological advancement and application value.

[0067] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The endpoints and any values ​​of the ranges disclosed herein are not limited to precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing a metal can packaging material, characterized in that: Includes the following steps, S1. After pretreatment of the metal substrate, rinse it quickly with deionized water, and then dry it thoroughly with hot air at 100-120℃ immediately. S2. A nanoporous adhesive layer is formed on one side of the pretreated metal substrate through a coating and curing process on the inner wall of the tank. S3. An ion-exchange anti-corrosion layer is formed on the nanoporous adhesive layer by deposition. After deposition, the metal substrate is gently rinsed with deionized water to remove loosely attached particles on the surface, and then dried at 80°C for 10 minutes. S4. A hydrophobic protective layer is formed on the ion exchange anti-corrosion layer by high-voltage electrostatic spraying and curing. S5. The metal substrate having the nanoporous adhesive layer, ion exchange anti-corrosion layer and hydrophobic protective layer on one side is processed into a metal tank as the inner wall. S6. Apply an outer wall decorative protective layer to the outer surface of the metal tank.

2. The method for preparing a metal can packaging material according to claim 1, characterized in that: In step S1, the metal substrate is tinplate. The pretreatment steps are as follows: the metal substrate is subjected to alkaline washing, acid washing and passivation treatment in sequence. The passivation treatment is carried out using a chromium-free passivation solution.

3. The method for preparing a metal can packaging material according to claim 2, characterized in that: The steps for alkaline washing, acid washing, and passivation treatment of the metal substrate are as follows: Immerse the metal substrate in a sodium hydroxide aqueous solution at a temperature of 55-65℃ and a concentration of 45-55 g / L for 2-4 minutes. Then, spray or rinse the metal substrate with running clean water until the water film on the substrate surface is uniform, without water droplets, and the pH value of the outflowing water is close to neutral. Next, immerse the water-washed metal substrate in a sulfuric acid aqueous solution at a temperature of 45-55℃ and a concentration of 140-160 g / L for 1.5-2.5 minutes. Finally, immerse the metal substrate in a chromium-free passivation solution at a temperature of 20-40℃ for 60-90 seconds.

4. The method for preparing a metal can packaging material according to claim 1, characterized in that: In step S2, the coating and curing process involves hydrolyzing and condensing tetrabutyl titanate under acidic catalysis, aging for 24 hours to form a stable composite sol, and then applying it to the highly active surface of the pretreated metal substrate using a dip-coating method at a uniform speed of 5 mm / s, followed by drying at 110-130°C for 20-40 minutes.

5. The method for preparing a metal can packaging material according to claim 1, characterized in that: In step S3, the deposition step involves immersing the metal substrate treated in step S2 as a cathode into an electrophoretic solution and electrophoretically electrophoresing it for 2 minutes at a constant voltage of 20V. The electrophoretic solution is prepared by dispersing 5wt% sodium montmorillonite and 1wt% conductive polyaniline in deionized water and mixing them thoroughly.

6. The method for preparing a metal can packaging material according to claim 1, characterized in that: In step S4, the coating and curing steps involve electrostatically spraying the modified acrylic resin onto the surface at an atomization pressure of 0.6 MPa and a spraying distance of 20 cm using high-voltage electrostatic spraying, followed by curing at 170-190°C for 25-35 minutes to form a hydrophobic protective layer.

7. The method for preparing a metal can packaging material according to claim 1, characterized in that: In step S5, the tank body is processed by forming the metal substrate into a tank body using a three-piece tank forming machine. The tank body welds are laser welded with a welding power of 1.8-2.2kW and a welding speed of 2.8-3.2m / min.

8. The method for preparing a metal can packaging material according to claim 1, characterized in that: In step S6, the outer surface is coated with an outer wall decorative protective layer by transporting the formed can in step S5 to the spraying line and fixing it on the rotating spraying bracket to ensure that the can rotate at a uniform speed. Then, a decorative primer and a clear topcoat are sprayed in sequence, and finally cured at high temperature to form an outer wall decorative protective layer.

9. A method for preparing a metal can packaging material according to claim 8, characterized in that: After the decorative primer is applied, it is leveled and pre-cured at 120-140℃ for 2-4 minutes, and then a hydroxyl acrylic resin topcoat is applied. The high-temperature curing is done by baking at 180-200℃ for 10-15 minutes.

10. A metal can packaging material, prepared according to the method for preparing a metal can packaging material according to any one of claims 1-9.