Improper Substrate Tension

The substrate is too loose or too tight during the coating process. 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. Process parameter factor: the tension setting value is incorrect. 2. Process parameter factor: tension sensor failure or zero drift. 3. Process parameter factor: the tension is not adjusted accordingly when the roll diameter changes (if there is no variable tension control system). 4. Process parameter factor: instantaneous tension is too large or too small during acceleration/deceleration. 5. Substrate surface condition factor: The surface tension, cleanliness and microscopic roughness of the substrate are the basic conditions for coating adhesion and leveling. When the substrate surface tension is lower than the surface tension of the coating liquid, wetting is insufficient and craters occur; surface contamination leads to local adhesion failure, which is the primary direction for troubleshooting coating defects.

1. Process parameter optimization and adjustment: set appropriate tension parameters according to the substrate variety. 2. Mold/tooling improvement and maintenance: calibrate the tension sensor. 3. Equipment inspection and system maintenance: implement taper tension control following the roll diameter. 4. Material/formulation optimization: moderate the acceleration/deceleration rate. 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 improper substrate tension 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.