Uneven Coating Stripes/Streaks (striation)

Strip-like uneven textures along the coating direction appear on the coating surface. When this defect appears in coating-formed products, it is usually closely related to the coating head precision, the rheological properties of the coating liquid, the substrate surface condition, or the curing process conditions. The distribution characteristics of coating defects (transverse/longitudinal/random) provide important clues for diagnosing coating head and curing system problems. Continuous occurrence will cause the functional performance of the coating to fall below standard, and coordinated troubleshooting is required from three aspects: coating liquid formulation, coating equipment, and curing process.

1. Mold/tooling factor: local clogging or burrs in the coating head gap. 2. Mold/tooling factor: vibration of the substrate when passing through the coating head. 3. Material/formulation factor: uneven pigment streaks in the coating liquid. 4. Equipment factor: the oven air nozzles blow directly onto the liquid coating. 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: ensure the coating head outlet is smooth and free of burrs and clogging. 2. Mold/tooling improvement and maintenance: stabilize the substrate conveyance to reduce vibration. 3. Equipment inspection and system maintenance: fully stir the coating liquid to prevent pigment streaks. 4. Material/formulation optimization: adjust the air speed of the first section of the oven to avoid direct impact on the wet film. 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 uneven coating stripes/streaks (striation) 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.