Fluorocarbon paint is composed of polytetrafluoroethylene resin, pigments, modifiers, etc. In actual production processes, the coating may develop line-like or grid-like cracks resembling a dried riverbed; this phenomenon is known as 'large cracking'. 'Large cracking' is usually caused by insufficient solvent during the melting of the paint film during the baking process after spraying. The following situations will exacerbate this phenomenon:
1. The time for the metal surface temperature to rise to 235°C is too long;
2. The flash drying speed of the paint film before baking is relatively too fast;
3. The profile is too thick, and the paint film is too thick;
4. Excessive pigment content, such as white or gray-white.
The following precautions should be observed to minimize the occurrence of "large cracking":
1. The primer should not be sprayed too thickly, it is recommended to have a dry film thickness of 5-10μm;
2. The primer should not flash dry too quickly before spraying the topcoat, otherwise, it may cause solvent dry absorption of the topcoat. Adding slow-drying solvent can extend the wetting time of the primer film;
3. The topcoat should not be too thick, it is recommended not to exceed 35μm and the evaporation should not be too fast. It is recommended to use slow-drying solvents, such as glycol monobutyl ether or butyl carbitol; generally, its flash drying time does not exceed 0.5 hours;
4. The process of heating the furnace to the set temperature should not be delayed; if it is too slow or if there are cold spots, it can lead to "large cracking".
