Most tinplate needs to be coated, and the quality of the coating directly affects the corrosion resistance of the metal can; some also require color printing. Coating properties include wetting and adhesion.
Coatings that do not wet or have holes are prone to corrosion at defect sites and are more prone to pitting corrosion compared to no coating. There are many factors that affect wetting, including the paint, coating conditions, and tinplate. The main causes caused by tinplate are as follows:
- Excessive oiling or uneven oiling.
- Surface adhesion of foreign objects such as mechanical oil, silicone resin, fine powder, moisture, etc.
- Surface state, aging, storage temperature, etc.
When the coating adhesion is poor, cracks, peeling, or flaking may occur during processing and deformation. Adhesion is also related to the paint and coating process, and the factors related to tinplate are as follows:
- Inhibition of tin oxidation and improvement of paint adhesion through passivation treatment. However, storage time and the number of repeated heating and baking affect adhesion.
- The influence of surface roughness.
- The influence of tin layer thickness.