Calendering wrinkles

Transverse or longitudinal wrinkles appear on the product surface; the film cannot remain flat when unfolded, showing creases or ripples. Wrinkles are more obvious after winding — wrinkled film layers stacking inside the roll causes the entire roll to be scrapped. Wrinkle formation is related to multiple factors such as uneven roll gap, unstable tension, and asymmetric cooling, and is one of the most common appearance defects of calendered film.

1. Mold/tooling factors: Uneven gap between calender rolls causes different material passing rates at various positions. 2. Process parameter factors: Uneven downstream stretching or winding tension. 3. Process parameter factors: Improper angle or tension during stripping. 4. Mold/tooling factors: Uneven roll temperature causes elongation differences. 5. Roll gap adjustment factors: Crown and cross-angle compensation of calender rolls is the core means of controlling the transverse thickness distribution of the film. Crown design is based on roll deflection calculations; if it does not match the actual process load, it will cause abnormal transverse distribution of film thickness — thicker in the middle and thinner at both ends, or an inverse bow-shaped distribution.

1. Process parameter optimization and adjustment: Adjust roll gap uniformity. 2. Mold/tooling improvement and maintenance: Check and adjust stretching and winding tension control. 3. Equipment inspection and system maintenance: Optimize stripper roll settings. 4. Material/formulation optimization: Ensure uniform roll temperature. 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 wrinkles is inconsistent speeds of various parts of the film surface passing through the roll nip or asymmetric tension distribution. The core of the solution is to ensure uniform roll gap and stable tension control — adjust the roll gap to eliminate local speed differences and optimize winding tension control to eliminate wrinkle sources.