微热压成型过程聚合物流动特性研究

Flow behavior of polymer during micro hot embossing

为了获得更好的压印效果,研究了聚合物在热压过程中的流动行为.采用有限元方法模拟了模具的占空比、聚合物的厚度、压印温度对压印力、压印时间及聚合物流场的影响.结果表明,随着模具占空比的减小,聚合物截面流型从单峰过渡到双峰,从陡峭过渡到平坦;随着聚合物厚度变薄,由于边界效应造成流动困难,需要施加的压印力迅速增加,并且压印力过小或压印时间不够将造成压印忠实度较低;对于非等温热压过程,当聚合物厚度较大时,由于模具压入区附近温度梯度较大,聚合物黏度降低,存在聚合物沿模具侧面爬升的现象.模拟结果与实验结果吻合.

The micro hot embossing process was simulated by finite element method （FEM） to investigate the flow behavior of polymer in order to get better imprint quality. The influences of mold duty ratio, polymer thickness, imprint temperature on the imprint pressure, imprint time and polymer flow field were analyzed. Simulation shows that with the decrease of mold duty ratio, the flow profile of polymer changes from one peak to dual peak and from craggedness to flatness. Due to boundary effect, when the polymer thickness decreases, the polymer becomes hard to flow, which results in the needed imprint pressure increases rapidly. Inadequate imprint pressure or short imprint time can lead to low pattern fidelity. In the non-isothermal embossing process, when the polymer thickness is relatively large, the polymer viscous becomes low around the extrusion area due to high temperature gradient, and the phenomena of polymer climbing along the mold side can be observed. The simulation results agree well with the experimental data.