Fluorocarbon paint is composed of polyvinylidene fluoride resin, pigments, modifiers, and other components. During actual production, the coating may develop linear or grid-like cracks resembling a dried-up riverbed, a phenomenon known as "alligator cracking." "Alligator cracking" usually occurs when the painted film melts during the baking process after spraying, caused by insufficient solvent. The following situations will exacerbate this phenomenon:
1. The time for the metal surface temperature to reach 235°C is too long;
2. The paint film dries too quickly before baking;
3. The profiles are too thick and the paint film is too thick;
4. Excessive pigment content, such as white or gray-white.
The following preventive measures should be followed to minimize the occurrence of "major cracking":
1. The primer should not be sprayed too thick, recommended dry film thickness is 5–10μm;
2. The primer should not flash dry too quickly before spraying the topcoat, otherwise it will cause the dry absorption of the topcoat solvent. Adding slow-drying solvents can extend the wetting time of the primer film;
3. The topcoat should not be too thick, recommended not to exceed 35μm. Evaporation should not be too fast; it is recommended to use slow-drying solvents such as butyl cellosolve or butyl carbitol. Generally, the flash drying time should not exceed 0.5 hours;
4. The process of heating the oven to the set temperature must not be delayed. Too slow heating or the presence of cold spots can both lead to "major cracking".
