Fabrication of flexible microlens array film using roll-to-roll process

Microlens arrays are a vital part of today's optical systems, and advances in fabrication technology have broadened microlens array applications. The roll-to-roll fabrication process has an advantage in its fast and mass replication of microstructures, and it is a good fit for fabricating devices based on flexible substrates. To investigate the roll-to-roll process in the making of microlens arrays of different radii in the same process, this study designs microlens arrays with radii ranging from 55 to 240 mu m and with a height of 15 mu m. The material for the lens is an ultraviolet curable resin with a refractive index of 1.5. The lens pattern is first transferred to an 80-mu m-thick stainless steel sheet through an etching process. The patterned sheet is then wrapped around a stainless steel roller for roll-to-roll fabrication of the microlens array film. The substrate for the microlens array is a polyethylene terephthalate film 188 mu m in thickness. When operating with a substrate forward speed of 0.251 m/min (1 r/min) and imprinting pressure of 0.6 MPa, the replication rates achieved for both the radius and the height of the microlens arrays are about 97%. Single-peak filling patterns are found with the small radii lenses, while dual-peak patterns are found in lenses with bigger radii. Overall, this study demonstrates the potential of roll-to-roll in three-dimensional pattern fabrications and its application in microlens array optical film fabrication.