Calendered sheet becoming brittle after cooling

The sheet becomes brittle and hard at room temperature and breaks. When this defect appears in calender molded products, it is usually closely related to process links such as roll gap adjustment, roll temperature distribution, feed uniformity, or winding tension control. Defects in calendered products often have transverse distribution characteristics, directly associated with roll surface condition and material bank behavior. Continuous occurrence will affect the film's appearance, thickness uniformity, and subsequent processing performance; troubleshooting must start from both roll system adjustment and the feed system.

1. Material/formulation factors: Insufficient plasticizer dosage or migration loss. 2. Material/formulation factors: Improper resin type selection (molecular weight too high). 3. Cooling/environmental factors: Cooling rate too fast causes molecular chains to freeze without relaxing. 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: Increase plasticizer dosage and check its migration stability. 2. Mold/tooling improvement and maintenance: Select resin with appropriate melt index. 3. Equipment inspection and system maintenance: Control cooling rate not too fast. 4. Systematic troubleshooting method: Troubleshooting of calendering problems follows the sequence "roll gap → roll temperature → feed → tension → cooling". First check and precisely adjust the roll gap crown and cross angle, then confirm the uniformity of each roll's temperature distribution, next check 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. 5. 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 sheet becoming brittle after cooling 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.