Research and application of a new rapid heat cycle molding with electric heating and coolant cooling to improve the surface quality of large LCD TV panels

The usage of rapid heat cycle molding (RHCM) has gained increasing attention in overcoming the limits of conventional injection molding (CIM) and improving the surface quality and mechanical properties of molded plastic products. In RHCM, the vario-thermal mold temperature control system is the key technique because it directly affects the molding cycle time and the final part quality. In this study, a new RHCM technology with electric heating and coolant cooling was studied in detail. Two different RHCM mold structures for a large LCD TV panel were proposed and designed. The numerical simulation method was used to analyze the thermal response of the mold cavity surface at the heating stage and the thermal response of the resin melt at the cooling stage. The heating/cooling efficiency of the proposed electric heating RHCM system was evaluated. The thermal expansion analysis of mold cavity was implemented and the fixation of the cavity in molds was also optimized. The results showed that the electric-heating mold with a separate cooling plate can efficiently enhance the heating efficiency. The thermal expansion of the cavity surface can be reduced by increasing the alleviating-gap between the cavity and the cavity-retainer plate. Then, the service lifetime of the electric-heating mold can be improved. A RHCM production line with electric heating for the large LCD TV panel was constructed. Both the simulation and test production results indicate that the proposed electric heating RHCM technique can realize high-temperature injection molding without increasing the molding cycle time. The surface appearance of the LCD TV panels was dramatically improved and the surface marks that usually occur in CIM process were eliminated completely. Copyright (C) 2009 John Wiley & Sons, Ltd.