Roll-to-roll micromolding of UV curable coatings

In this study, fast and continuous fabrication of microscale structures by roll-to-roll UV imprinting or micromolding is demonstrated on a 121 mm wide web. This process is enabled by a UV curable thiol-ene-acrylate resin system, following the work of Stadlober and coworkers. A series of formulations were prepared with fast curing speeds at ambient conditions, low viscosities, and tunable mechanical properties. The rate and extent of curing as a function of the formulation composition were investigated with Fourier transform infrared spectroscopy. Consistent with the past work, we show that the thiol-ene-acrylate formulations reached high double bond conversions (> 80%) with the maximum conversion increasing with the relative thiol content and decreasing with the viscous urethane acrylate oligomer content. The double bond conversion of the patterned coatings (in contact with the mold) is shown to be ~ 80% for a range of UV lamp powers and web speeds up to 2.7 cm/s. Areas of the coating not covered by the mold required higher UV lamp power and/or lower web speeds to cure to a tack-free state. Microscale channels and arrays of recessed wells with various dimensions and pattern densities were continuously fabricated. Our findings show the successful use of a tetrafunctional thiol in the thiol-ene-acrylate resin system. We also discuss guidelines for the selection of processing conditions for the manufacturing of structured plastic substrates using roll-to-roll imprinting processes, opening up potential new applications.