As the demand for food and beverages continues to grow, the packaging market is also expanding, with metal packaging materials accounting for approximately 15% of the total global packaging materials used. According to market intelligence reports, the global metal can market’s revenue reached a cumulative total of $53.37 billion in 2023. The production scale of metal cans for food and beverages is also steadily increasing. The potential corrosion behavior of metal packaging can significantly affect the taste of food, leading to a decline in food quality. In common tinplate cans, metal corrosion is an electrochemical process of oxidation-reduction. When the electrode potential of the metal is negative, oxidation occurs, causing the metal to corrode and dissolve. Conversely, when the electrode potential of the metal is positive, it protects the metal from corrosion. Food and beverages in daily life have complex compositions, with significant fluctuations in pH values, resulting in electrochemical processes differing greatly from standard electrode reactions. Vegetables often contain high concentrations of nitrates, and beverages generally contain processed sugars and other components (carbon dioxide in carbonated beverages, organic acids in functional beverages), which can exhibit strong corrosiveness. When food and beverages are acidic, the anode of tinplate cans exhibits metal dissolution reactions, while the cathode mainly shows H2 reduction reactions. When the environment of food and beverages is neutral, oxidation-reduction reactions primarily occur.
In practical production applications, metal packaging typically undergoes organic coating on the surface of tin-plated thin steel sheets, where the organic coating plays the main role in corrosion protection, preventing direct contact between metal and food. During the production of coated iron, the organic coating may have pores, causing the coating to fail. Xia Dahai et al. studied the corrosion behavior of tin-plated thin steel sheets coated with epoxy-phenolic in functional beverages. In the experiment, the pH value of a certain brand of functional beverage was between 3.0 and 3.2, and it also contained various food additives. On the 5th day of the immersion test, corrosion began to occur, with the organic coating developing micropores, leading to localized corrosion at the electro-couple formation site; subsequently, the tin-plated layer beneath the coating corroded under the influence of the functional beverage. Once the tin-plated layer is corroded, the base metal carbon steel with higher electrochemical activity undergoes dissolution, converting the corrosion process.
Clearly, the quality of the protective coating is crucial for the corrosion resistance of metals. Metal coating is an effective method to prevent metal corrosion. Plastic films adhered to metal substrates can isolate the metal can body from food and beverages, preventing ion reactions. Metal-coated packaging has stable chemical properties, fewer pinholes on the surface, is environmentally friendly, cost-effective, and can undergo various film treatments. Song Weiwei et tested the performance of coated iron cans and metal-coated iron cans under the same conditions using electrochemical impedance spectroscopy and other methods. They found that compared to coated iron cans, metal-coated iron cans have much higher electrochemical impedance, better sulfur resistance, and superior corrosion resistance at room temperature. Therefore, for food and beverages, metal-coated packaging is an ideal green packaging technology.
