Visualization Analysis of Wrinkle Generation Phenomenon in PP Decorative Sheets (Part 2) ―Identification of Interfacial Thermal Resistance by Measurement of Temperature Change inside Decorative PP Sheets and at Flow Front

The formation of wrinkles on decorative PP sheets is a typical problem of in-mold injection molding. In a previous paper, through visualization analysis, we showed that the decorative sheet slips on the mold surface and deforms along the flow direction during in-mold injection molding. In simulation of the amount of this deformation, the interfacial thermal resistance (ITR) of each mold surface during in-mold injection molding should be considered in order to calculate changes in the sheet temperature. Therefore, in this study, we developed a method to measure the temperature inside the decorative PP sheet and the temperature of the flow front resin contacting the sheet using an infrared temperature sensor. We conducted experiments using a visualization mold model to compare (a) the results of changing the temperature inside the measured sheet and the temperature of injected resin with (b) the results of calculating the temperature distribution along the sheet thickness by virtually changing the ITR on each sheet interface. As a result, we successfully identified the heat transfer coefficients of the injected resin-sheet and sheet-cavity surface interface, which were 2800 W/m2・K on the injected resin-sheet interface and 1000 W/m2・K on the sheet-cavity surface interface.