Poor Leveling

The coating cannot level to form a continuous smooth film surface in the wet film stage, showing brush marks, knife marks or streaks. Poor leveling is a fundamental defect in coating forming, directly affecting the appearance quality and functional uniformity of the coating. A poorly leveled coating shows obvious thickness fluctuations under the microscope, and the functional performance (such as conductivity, barrier property) correspondingly shows local deviations.

1. Comprehensive factor: the leveling stage after coating is too short. 2. Material/formulation factor: drying is too fast. 3. Material/formulation factor: the coating liquid viscosity is too high. 4. Material/formulation factor: uneven distribution of substrate surface energy affects the spreading of the wet film. 5. Curing process factor: the curing temperature and time determine the completion degree of the coating crosslinking reaction — insufficient temperature or time leads to incomplete curing (tacky, low hardness, poor solvent resistance), while excessive temperature or time leads to over-curing (embrittlement, yellowing, cracking), which requires precise matching to the curing window of the coating liquid system.

1. Process parameter optimization and adjustment: extend the residence time of the leveling section (reduce line speed/increase leveling section length). 2. Mold/tooling improvement and maintenance: use a slow-volatilizing solvent. 3. Equipment inspection and system maintenance: appropriately reduce the coating viscosity. 4. Material/formulation optimization: improve the substrate surface treatment quality. 6. 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 the 5Why analysis method to trace the root cause, and solidify the 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.

This problem is a typical manifestation of poor leveling in coating forming. The core of the solution lies in ensuring the substrate surface condition, optimizing the rheological properties of the coating liquid, and precisely controlling the curing process conditions. It is recommended to start from the two aspects of substrate and coating liquid, and gradually troubleshoot to the coating equipment and curing system.