Study On Morphology Of Supercritical Microcellular Injection Molded Polycarbonate Parts

Microcellular injection molding involves all factors of injection molding and supercritical fluid (SCF), and it is hard to control the processing stability and repeatability. Therefore, the relationships between processing parameters, morphology structure and final performance are considered as a key focus.In order to take advantages of microcellular injection molding processing and obtain higher performance-cost ratio products, the processing parameters effects on microcellular injection molded PC (polycarbonate) parts (supercritical N₂ as foaming agents) were studied by experiment and numerical simulation methods, espically the effects on morphology and final products qualities in this paper. The finished jobs are as follows.First, square microcellular injection molded PC parts with SCF of nitrogen were made based on the orthogonal array of six parameters and three levels of Orthogonal Experiment Method.Second, the microcellular injection molded PC parts were characterized by Scanning Electronic Microscope (SEM), Electronic Balance, Venire Caliper and the software of SmileView. Distributions of cell morphology, skin-layer or sandwich layer were investigated, and the distribution reasons were discussed. Also different methods of cell density characterize were compared.Third, the effects of microcellular processing parameters (melt temperature, mold temperature, injection speed, SCF weight ratio, back pressure, pre-plasticizing volume) on cross-section cell density which is the number of cells in every square centimeter of cross-section, cell diameter, skin-layer relative thickness and foamed PC parts' weight were studied by experiments and numerical simulation. As for cell diameter near gate location, experiment results have good accordance with simulated results. By orthogonal experiment results and calculation, the feasible processing parameters of the L₁₈ (3⁶) table were found.Finally, the surface defects of microcellular injection molded parts were studied based on SEM experimental results. It was found that morphology of swirl marks, silver streaks has relation with cell morphology and surface roughness.