SIMULATION OF SQUEEZING FLOW DURING HOT EMBOSSING OF POLYMER MICROSTRUCTURES

摘要

In this paper, numerical simulation of the hot embossing process with non-isothermal embossing conditions (i.e. the initial temperature of the polymer substrate is the room temperature) was carried out to observe the flow patterns of thin PMMA films into micro cavities. Different thicknesses of PMMA films, from 1 μm to 400 μm, were used in the simulation. It was found that, as the thickness of the PMMA film reduced the filling mechanism varied. For PMMA films with a thickness above 100 μm, the polymer flow climbed along the wall of the heated die, and then compressed downward and squeezed outward. In contrast, for a smaller thickness of less than 50 μm, the flow was uniform and the wall climbing flow was absent. This size effect was explained using the temperature distribution of the polymer substrate during the embossing process. For a thickness above 100 μm, the high temperature zone was localized in the vicinity of the die wall, and consequently localized wall climbing flow resulted.