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For LCDs, the mainstream COC film production method is melt extrusion casting + biaxial stretching (BCOP); the process window is extremely narrow, requiring micron-level precision and zero-defect control. 1. Extrusion and casting: A precise balance of temperature/pressure/speed is required; the temperature range is very narrow. The melting temperature of COC is 240–280°C, and even a variation of ±1°C can lead to sudden changes in melt viscosity, uneven film thickness, and excessive birefringence. Die and cooling: A precision die lip gap tolerance of ±0.5μm is required, along with a temperature uniformity of ±0.5 for the casting rolls℃ ； Uneven cooling generates internal stresses and uneven in-plane birefringence, which directly leads to Mura in LCD displays. Uniform thickness: The base film thickness is 25–100μm, with a tolerance of **≤±1μm**** ； The larger the width (e.g., 1500mm+), the more difficult it is to control uniformity. Defect-free requirement: the film surface must be free of any crystals, bubbles, streaks, or precipitates; otherwise, bright spots/dark spots/linear marks will form in the LCD backlight. 2. Bidirectional stretching (BCOP): Precise matching of stress and optical control is required for the stretching ratio, temperature, and rate; otherwise: uneven stretching → sudden local birefringence, film surface wrinkling, and fracture. Residual stress → warping and optical drift during subsequent coating/adhesion/use. COC has much poorer stretchability than PET, is prone to cracking, and its stretching yield is inherently lower than that of PET. 3. Surface and adhesion: The challenges associated with low surface energy and multi-layer composites – COC has an inherently very low surface energy