Mass-production of antireflection films via RTR-UV-NIL and their various applications

Methods for transferring nanoscale patterns include nanoimprinting, soft lithography, and nanosphere lithography. Soft lithography is a two-dimensional pattern transfer technique. In contrast, nanosphere lithography transfers the shape of arranged polystyrene spheres and is therefore a three-dimensional shape transfer technique; however, it offers limited freedom in terms of shape. Therefore, a technology to transfer the antireflective structure of a moth's eye onto a large surface area has been developed using nanoimprint lithography (NIL), which enables low-cost mass production of nanopatterns. For large-area transfer, a roll mold was used in conjunction with roll-to-roll (RTR) ultraviolet NIL (UV-NIL), which transfers in a printing-like manner. A UV-curable resin was used as the transfer resin, enabling high-speed transfer at room temperature. The moth-eye structure was created on the roll mold by irradiating glassy carbon (GC) with an oxygen-ion beam. To form the moth-eye structure in the roll mold, an aluminum roll with a diameter of 30 cm and a length of 1.5 m was prepared and a thin GC film was formed on the side of the roll by sputtering. The surface was subsequently roughened by oxygen reactive ion etching to form the moth-eye structure. The roll mold was subjected to a release treatment, and the moth-eye structure was transferred onto a triacetylcellulose film using RTR UV-NIL. The UV-curable resin used here contained a fluorine material that made the moth-eye structure water-repellent after transfer. The film with the transferred moth-eye structure exhibited a low reflectance of 0.1% across the visible light range, and its contact angle with water exceeded 150°. When this moth-eye-structured film was applied to both sides of a window, it was found to be antireflective and to prevent water droplets from adhering. This water-repellent moth-eye-structured film repels rain and water, thereby improving visibility, and is therefore expected to be used on ships.