Core process principle: The longitudinal stretching unit adopts a multi-point stretching machine (MDO), which achieves step-by-step and precise stretching of thick sheets through the coordinated cooperation of multiple preheating rollers, multi-point stretching rollers, and cooling rollers. Technical advantages: The multi-point stretching process can effectively reduce the concentration of tensile stress, improve the longitudinal stretching uniformity of the film, avoid local fracture and uneven performance caused by single point stretching, and significantly optimize the longitudinal mechanical properties and thickness uniformity of the film. The stretching ratio can reach 3.4-7 times. Commercial value: Addressing the pain points of film breakage, increasing the yield rate to over 95%, and significantly reducing production costs.