Calendered film blocking after winding (blocking)

During winding, various defects occur: too loose tension causes loose roll slipping, too tight tension causes film surface stretching deformation, uneven roll edges in plum-blossom shape, core wrinkling, etc. Poor winding directly affects product storage stability and subsequent processing — loose rolls have film layers sliding during storage producing wrinkles, tight rolls increase film surface internal stress causing shrinkage deformation. Winding tension control is the last key process of the calendering production line.

1. Material/formulation factors: Too much plasticizer or surface precipitates. 2. Process parameter factors: Winding tension too large causes tight interlayer contact. 3. Cooling/environmental factors: Insufficient cooling, winding while still warm. 4. 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. 5. Feed uniformity factors: The temperature uniformity of the calender feed and the shape stability of the material bank directly affect the uniformity of feeding into the roll nip. A material bank that is too narrow, skewed, or unevenly rolling all cause transverse thickness abnormalities in the product; the temperature and flow rate of the banbury or extrusion feed must be kept stable.

1. Process parameter optimization and adjustment: The synergist should be used in appropriate amount. 2. Mold/tooling improvement and maintenance: Reduce winding tension. 3. Equipment inspection and system maintenance: Fully cool the product to room temperature before winding. 4. Material/formulation optimization: If necessary, add anti-blocking interleaving paper in the roll or apply release agent treatment. 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.

This problem is a typical manifestation of calendered film blocking after winding (blocking) in calender molding. The core of the solution lies in precise adjustment of roll gap compensation, uniform control of roll temperature distribution, and assurance of feed system stability. It is recommended to start troubleshooting from roll system parameters and gradually go deeper into the equipment and formulation levels.