Tin can is dissolved in canned food, so the thickness of the coating on the inner wall of the food tins is generally between 3.5 and 6.0 g / m2. Within this thickness range, the coating has a certain porosity. The liquid in the food safe tins contents penetrates the surface of the tin layer through these pores, slowly dissolves the tin to form tin ions, and then reaches the intention of extending the shelf life of the empty tins .
For acid foods, such as asparagus, bamboo shoots in clear water, broccoli, etc., the coating on the inner wall of the empty tins can be printed using the "composite coating layer" process. These plants have a high protein content. In the process of canning and canning, the sulfur-containing amino saddle decomposes more hydrogen sulfide and has a strong sulfuric acid corrosion on the food tins wall. The "composite coating layer" is the method of "three coatings and two baking" in the printing process. That is, a layer of primer with strong adhesion and plasticity based on epoxy resin and xylene resin is printed on the outer surface of food tins. After baking and curing, the epoxy resin and phenolic resin-type paint are overcoated twice. (The bottom and lid of the empty tins can be turned on immediately after the second coating.) After the "three coatings and two bakings" printing , the total thickness of the coating reaches 10-13 g / m2, which increases the denseness of the coating and the porosity simply disappears. The coating on food safe tins not only has excellent adhesion, but also has good flexibility and ductility, and has outstanding can-making functions