Cellular distribution and warpage deformation in double-sided in-mold decoration combined with microcellular injection molding process

A single-sided in-mold decoration combined with microcellular injection molding (S-IMD/MIM) process uses one decorative film to cover apparent defects of light-weight plastic products. The S-IMD/MIM process results in unbalanced temperature and uneven cellular distribution, and consequently large warpage deformation. In order to reduce the warpage, an innovative method is proposed by utilizing double-sided in-mold decoration combined with microcellular injection molding (D-IMD/MIM) process. The method sticks two decorative films to both inner walls of mold cavity for injection molding. This work takes a spline as a sample for numerical simulation and molding experiment. The results show that D-IMD/MIM process brings about balanced temperature distribution inside melts such that cells inside splines are stratified and symmetrically distributed. In such a case, there is less thermal stress inside spline as well as small warpage deformation of spline. By comparison with S-IMD/MIM spline, D-IMD/MIM spline has the warpage with a 71.68 % of reduction. It indicated that D-IMD/MIM process may effectively suppress warpage deformation of molded products.