The reason why tinplate can come into contact with food is not because iron is rust-proof, but because the tin layer provides protection
Tinplate is essentially a low-carbon cold-rolled steel sheet with tin plating on both sides. Its safety in contact with food is based on two aspects:
Tin layer isolation: Food does not directly touch the steel substrate, reducing the leaching of iron ions;
Passivation + complete plating: The surface passivation treatment + complete tin layer make it difficult for acidic media to penetrate into the iron matrix.
However, tinplate is not "never reactive". Once the plating has pinholes, scratches, inadequate weld coating, or when high-acid foods are stored for a long time, local corrosion and increased tin migration may occur.
So what the national standard regulates is "migration amount", not "if the material is called tinplate, it is automatically safe".
