Effect of Films on In‐Mold Decoration and Microcellular Foaming Injection Molding Parts: Cell Structure, Surface, Warpage, and Mechanical Properties

ABSTRACT The in‐mold decoration and microcellular foaming injection molding (IMD‐MIM) process was proposed to solve the apparent quality problem of polypropylene in microcellular foaming injection molding. Based on physical experiments and finite element simulation, stainless steel (ST) and polyethylene glycol terephthalate (PET) decorative films were selected for analysis, and the influence of the type and thickness of the decorative films on the cell structure, surface morphology, warpage deformation, and mechanical properties was revealed. The results show that the surface quality of the samples coated is significantly improved, and the asymmetric temperature field caused by the films changes the structure and distribution of the cells. The cell density on the coated side is higher than that on the non‐coated side, and the average cell diameter is smaller, and the foam core layer is shifted to the coated side. The warpage caused by ST film is larger, up to 2.836 mm. With the intervention of ST film and PET film, the impact properties of the samples have little change, but the tensile and flexural properties of the foamed samples have been effectively improved. The tensile strength increased by 28.6% and 25.9%, while the flexural strength increased by 28.6% and 28.1%, respectively. This study provides new insights into the comprehensive optimization of the structure and performance of polypropylene microcellular foaming materials and provides support for the development and application of lightweight materials in the future.