Using a partial thin-wall cavity with an ultra-thin-wall (thickness: 0.05mm) section at the center of the cavity, investigations were conducted to clarify the effects of changes in rise time of the screw injection speed on the fillability of ultra-thin-wall sections and the thickness distribution. Using a high-response infrared thermometer (response time: 8μs, 95%), the dependence of changes in the temperature of the flow-front area on the rise time was clarified through polypropylene molding experiments. The following results were obtained.
Improvements in the rise time was confirmed to be an effective means for enhancing the fillability of ultra-thin-wall areas and reducing the thickness of the molded product. By using a high response thermometer, the characteristic resin temperature changes in the flow-front area during ultra-high-speed filling were successfully extracted in detail for the first time.
For set rise times of 0ms and 30ms (actual measured values were 11.2ms and 27.5ms, respectively) the temperature difference in the flow-front area was about 25°C.
This temperature increase in the flow-front area markedly reduced viscosity and allowed filling of the ultra-thin-wall section in a short period of time, and also served to reduce the thickness by the reduction of in-cavity pressure.