Haze Surge of Calendered PP Transparent Sheets

After producing PP transparent sheets for a period of time, the haze suddenly increases. When this defect occurs in calendered products, it is usually closely related to process links such as nip adjustment, roll temperature distribution, feed uniformity, or winding tension control. Defects of calendered products often have transverse distribution characteristics and are directly associated with roll surface condition and material bank behavior. If it persists, it will affect the film's appearance, thickness uniformity, and subsequent processing performance, and needs to be investigated from both roll system adjustment and the feed system.

1. Mold/tooling factors: an extremely thin precipitate film (such as lubricant or low-molecular PP degradation products) on the roll surface is transferred to the product surface. 2. Nip adjustment factors: The 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 calculation; if it does not match the actual process load, it will lead to abnormal transverse distribution of film thickness—thicker in the middle and thinner at both ends, or reverse bow-shaped distribution. 3. Feed uniformity factors: The temperature uniformity of the calender feed and the stability of the material bank shape directly affect the uniformity of nip feeding. A bank that is too narrow, skewed, or unevenly rolled will all cause transverse thickness abnormalities in the product; it is necessary to ensure the temperature and flow stability of the internal-mixer or extruder feed.

1. Process parameter optimization and adjustment: Stop the machine to clean the roll surface. 2. Mold/tooling improvement and maintenance: Check and optimize the lubricant/release agent content and heat resistance in the formulation. 3. Systematic troubleshooting method: Troubleshooting of calendering problems follows the order of "nip → roll temperature → feed → tension → cooling". First check and precisely adjust the nip crown and cross angle, then confirm the uniformity of the temperature distribution of each roll, then verify the feed bank shape and rolling behavior, further adjust the winding tension control parameters, and finally optimize the cooling roll temperature and contact method. Change only one variable at a time to confirm the effect. 4. 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 haze surge of calendered PP transparent sheets in calendering. The core of the solution lies in the precise adjustment of nip compensation, uniform control of roll temperature distribution, and stability assurance of the feed system. It is recommended to start troubleshooting from the roll system parameters and gradually go deeper into the equipment and formulation level.