Metal, as one of the common packaging materials, occupies an important position in industries such as food, beverages, pharmaceuticals, oils, chemicals, and cosmetics due to its recyclability, environmental friendliness, excellent ductility, formability, barrier properties, decorative properties, and comprehensive protection. Compared to plastics and glass, metals have poorer corrosion resistance and unstable chemical properties, making them prone to corrosion. Additionally, heavy metal ions such as Pb, Be, and Sn that may be present in metal materials can contaminate food, posing certain hazards to human health. In traditional metal canning processes, internal coating treatments are applied to prevent metal corrosion. However, substances like bisphenol A and environmental hormones present in coatings may leach out under specific conditions. If the leaching exceeds the standard limits, it can harm human health. The high-temperature drying process of coatings consumes a significant amount of thermal energy, leading to issues with VOC emissions and recovery treatment. Therefore, compared to traditional spray techniques, metal coating technology aligns more with the concept of green packaging development. It involves adhering polymers to metal substrates through thermal fusion or bonding methods, possessing both metal and film characteristics. Importantly, as no adhesives or solvents are used in its production, it reduces exhaust emissions.
Metal coating technology mainly consists of two types of substrates: metal substrates and polymer films. Chromium-plated steel, tinplate, cold-rolled thin steel sheets, as well as copper and aluminum plates, can all be used as coating substrates in metal coating processes. Chromium-plated steel, due to its low cost, excellent coating performance, and processing and corrosion resistance comparable to tinplate, has become the primary material for coated steel today. The materials used for composite films are also quite extensive. Depending on different usage requirements, materials like nylon, PP, PE, PET, PVC, and VCM can be chosen as film materials.
