Influence of using pulsed cooling for mold temperature control on microgroove duplication accuracy and warpage of the Blu-ray Disc

The usage of pulsed cooling for mold temperature to improve the molding process has been gaining increasing attention. In this study, Blu-ray Disc substrates, adapted for the commercial format media, were injection molded by combining pulsed-cooling technology. When applying pulsed cooling, coolant circulation is usually stopped during the melt-filling process and the mold opening and closing period. This leads to the additional cavity surface temperature increase and may vary part qualities. The correlations of mold temperature, cycle time, and pulse cooling duration with microgroove duplication accuracy and substrate qualities such as warpage in different directions were investigated in details. Measured results were also compared with those of injection-compression molded Blu-ray Disc using conventional cooling. The experiments showed that by using pulsed cooling in a proper manner one may manufacture Blu-ray Discs with lower warpage, higher accuracy in microgroove replication meanwhile reducing coolant temperature by 8 °C and shortening the cycle time by10% as compared to the conventional-cooling process. The usefulness of pulsed cooling and its potential in improving part quality and reducing cycle time during injection molding have been successfully demonstrated.