Investigation of ink transfer in a roller-reversal imprint process

Roller imprint is considered as one of the processes suitable for patterning on a large-area flexible substrate, which is critical for macroelectronics manufacturing. In contrast to other published roller imprint processes (such as hot-embossing roller imprint or ultraviolet roller imprint), the roller-reversal imprint (RRI) process investigated in this paper starts with pattern coating of an ink (mostly a liquefied electronics material, such as a semiconductor polymer) on a mould roller and ends with transferring the ink already patterned on the roller to the substrate, so it can obtain micropatterns with a precise profile yet leave no residual film on the substrate. One of the critical issues in obtaining patterned ink on the substrate with the required profile by the RRI process is to ensure a complete ink transfer from the microcavities on the mould roller onto the substrate. In this paper, a mathematical model is proposed to analyze the mechanics of the ink transfer, and a criterion for a complete ink transfer is derived. Furthermore, the effects of imprint force on the ink transfer are also demonstrated by an analysis of the elastic deformation of the substrate. The simulations and corresponding experiments show that the ink transfer in the RRI process is strongly dependent on the ratio of work of adhesion at the ink-mould and ink-substrate interfaces, and the critical ratio for a complete ink transfer is determined mainly by the profile of microcavities on the mould featured by the aspect ratio and the sidewall angle. The ink transfer model can be used to select proper materials (including the ink, surface energies of the mould roller and substrate) in the RRI process, and can also be regarded as a guideline for profile designing of the microcavities on the mould roller used in the RRI process.