Large-area Peeling of Fluoropolymer Coating Cracking After Coating

Fine cracks appear on the coating surface, with crack directions randomly or parallelly arranged, and in severe cases forming a network of cracks. Coating cracking is the result of internal stress exceeding the fracture toughness of the coating—the difference in shrinkage rate between the coating and the substrate generates interfacial stress during curing, an overly thick coating increases the absolute value of stress, and an overly fast curing speed leaves no time for stress relaxation. A cracked coating not only loses its protective and decorative functions, but the cracks also become channels for corrosive media to invade the substrate.

1. Material/formulation factors: the fluororesin is extremely non-stick to the substrate surface, and the fluororesin does not melt and spread well when superimposed with the primer layer. 2. Curing process factors: Curing temperature and time determine the completion degree of the coating crosslinking reaction—insufficient temperature or insufficient time leads to incomplete curing (tacky, low hardness, poor solvent resistance), excessive temperature or excessive time leads to over-curing (embrittlement, yellowing, cracking); the curing window of the coating fluid system must be precisely matched.

1. Process parameter optimization and adjustment: Strengthen chemical activation or etching treatment of the substrate. 2. Mold/tooling improvement and maintenance: Use primer adhesives containing chemical anchoring groups. 3. Systematic troubleshooting method: Troubleshooting of coating problems follows the order of "substrate → coating fluid → coating head → curing → environment". First check the substrate surface tension (corona treatment effect) and cleanliness, then verify the coating fluid viscosity, solid content, and degassing status, then check the coating head gap and cleanliness, further verify the curing temperature and time, and finally evaluate the influence of ambient temperature, humidity, and cleanliness. 4. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points. Establish a regular equipment maintenance system and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

The essence of coating cracking is that the internal stress exceeds the fracture toughness of the coating. The core of the solution is "stress reduction + toughening": control the coating thickness to avoid excessive stress accumulation, adopt mild curing conditions to allow stress relaxation, add toughening agents to improve the coating's fracture toughness, and select a coating system with a shrinkage rate close to that of the substrate.