In the multilayer co-extrusion process, two or more materials are simultaneously brought together and layered in a single extrusion process. When co-extruding two polymers with different rheological properties, uniformity control of the flow layer at and downstream of the confluence is vital for the quality of multilayered film products. This work aimed to investigate the effects of viscosity and elasticity of the co-extruding polymers on the layer uniformity at the confluence. We conducted a PC/PMMA/PC three-layer film co-extrusion experiment to observe the flow of polymer melts at the confluence in the die. The thickness variation of each layer along the flow was recorded through a viewing window structured on the die wall using a camera. In addition, the flow and stress field analyses of PC/PMMA/PC co-extrusion were performed using POLYFLOW software. The research results demonstrated that oscillation of flow velocity in machine direction along the PC/PMMA interface accompanying a wavy distribution of layer thickness along the flow may occur due to the differences of viscosity and elasticity between the PC and PMMA. Although slipping may occur at the PC/PMMA interface, which reduces the shear stress between the PC and the PMMA layer boundaries, the shear stress distribution crossing the PC/PMMA interface is not continuous. The imbalance of the shear stresses along the adjacent PC and PMMA boundaries expands with the extrusion rate, which can cause the interface to distort. To avoid the occurrence of interfacial instability, the length of die channel downstream the confluence must be shortened as much as possible, and the extrusion rate must be lowered.

The slot coating process in the production of polymer films has a wide range of applications. However, the process cannot be systemized. This study used the computational fluid dynamics software Polyflow to analyze the slot coating process and investigate the influence that the process parameters have on the characteristics of thin-film coating to reduce the time and cost consumed in the experimental methods. The rheological characteristics of the non-Newtonian fluid used in this study were first identified by conducting experiments, and then configured in the simulation software for fitting with mathematical models. In addition, the models of the slot coating process were constructed, and the Arbitrary Lagrangian-Eulerian (ALE) calculation methods were then used in the Polyflow software. The simulation results were then compared to the experimental results and the findings reported in relevant literature, to determine the influence that the process parameters have on the characteristics of thin-film coating. The simulation results were represented graphically in a coating window plot. The comparison results indicate that the viscosity-shear rate characteristic of the material in the shear rate range of optical film coating is an excellent fit for the Cross Law. When the coating speed is too high or the amount of fluid supply is insufficient, phenomena such as break lines, uneven thickness, and air entrainment can occur.

Developing the interior structures of polymer films is essential for creating novel functions of such films. This study investigates the effects of extension parameters and processing procedures on the super-structure of a polypropylene (PP) film. An biaxial extension device is also designed and fabricated to analyze the effects of annealing, extension temperature, extension rate and other parameters on the super-structures of PP films. Based on super-structure analyses, the relationships between extension parameters and film structures are determined, and an extension process that involves a second time stretching procedure is suggested. Experimental results indicate that void structures can be generated by biaxial extension at the interface between the crystalline and amorphous regions in a film. The mechanical strength of the film is also affected by stretching and become highly oriented. Although a low extension temperature can increase the number of void structures generated at a low extension ratio, structure sizes are dispersed. Additionally, voids with uniform size can be obtained when the film is stretched at a high temperature; however, it needs a high extension ratio to promote the formation of void structures. As for annealing treatment, when the annealing temperature increased, the size and quantity of the spherulites that were formed in films by annealing also increased, but these films tend to have similar sizes and numbers of void structures. Based on the experimental results, this study also describes how parameters influence the void structures of a PP film created during the extension process. Analysis results further demonstrate how extension parameters and processing procedures can be adjusted to improve the fabrication of PP films.