Uneven coating thickness

Calendered film thickness variation along the width direction exceeds allowable tolerance; transverse thickness variation manifests in multiple distribution patterns such as one end thicker and the other thinner, or middle thicker and both ends thinner. Uneven thickness directly affects the uniformity of mechanical properties and consistency of optical properties of the film — thick areas have higher strength but reduced light transmittance, thin areas are easily stretched and broken. In subsequent stretching and winding processes, uneven thickness also causes deviation and wrinkles.

1. Mold/tooling factors: Uneven coating head gap adjustment (knife coating). 2. Comprehensive factors: Coating liquid supply fluctuation. 3. Process parameter factors: Uneven substrate tension causes gap changes when passing the coating head. 4. Material/formulation factors: Coating liquid viscosity fluctuates with temperature. 5. Curing process factors: Curing temperature and time determine the completion degree of the coating crosslinking reaction — insufficient temperature or time causes incomplete curing (tacky, low hardness, poor solvent resistance), excessive temperature or time causes over-curing (embrittlement, yellowing, cracking); the curing window of the coating liquid system must be precisely matched.

1. Process parameter optimization and adjustment: Precisely adjust coating head gap and regularly check wear. 2. Mold/tooling improvement and maintenance: Stabilize liquid supply pump flow. 3. Equipment inspection and system maintenance: Optimize tension control system to ensure the substrate passes the coating zone flat. 4. Material/formulation optimization: Control coating liquid temperature to keep its viscosity stable. 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 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 transverse thickness unevenness of calendered film is uneven distribution of roll gap along the axial direction. The core of the solution is "precise compensation": compensate roll deflection through precise adjustment of crown and cross angle, combined with real-time feedback fine-tuning from the online thickness gauge, to ensure the roll gap is uniform and consistent under working load.