Why does the surface of iron cans and boxes need to be oiled?

The iron material of iron cans and boxes, whether printed or not, has the same process - oiling. So many people don't understand why iron materials need to be oiled before making iron cans? What are the benefits of oil on iron cans and boxes?
Firstly, the primary purpose of oiling is to protect iron cans and boxes. After the surface of the iron can and box is coated with oil, it can effectively isolate the contact between the tinplate and moisture in the air, preventing rust on the iron can.
Secondly, after the surface of the tin can and iron box is oiled, the printing color becomes more vivid, which also makes the metallic luster of the tinplate more prominent.
The oil commonly used on the surface of iron materials includes varnish and gold oil. The varnish is transparent and does not affect the original printing effect of the iron material, but instead makes the color more vivid; And gold oil is a light golden color, usually used inside iron cans and boxes. In addition, the oil on the surface of the iron box is also composed of special inks such as matte oil, matte oil, wrinkle oil, and explosive oil.