Fabrication of stochastic nanostructures on polymer webs for AR-effect using roll-to-roll equipment
Self-organized nanostructures can be created on polymer substrates by applying a plasma or ion treatment. This technology may be used for anti-reflection (AR) applications. Compared to conventional AR-coatings, the nano-structures have a high potential for both cost reduction and increase of performance. A really cost-effective production of polymer films with AR-properties using this technology requires an in-line implementation of this process into a roll-to-roll equipment. The technology should include either a plasma source or an ion source. It allows high productivity, treatment of substrates with process widths of typical industrial web coaters (one meter and more) and can easily be adapted to existing web coaters. A source complying with all these requirements was detected: a dual magnetron with full poisoned (oxidized) targets. The hot negative oxygen ions created on the target surface treat the polymer surface and cause the development of stochastic nano structures. By applying of pre-coating, the shape of structures and hence the optical properties can be tuned. The process was installed in a pilot-scale roll-to-roll coating machine with a process width of 600 mm. Using the TiO2 pre-coating and subsequently treatment on PET, an optical transmission of 93.5 % at a wavelength of 550 nm by a winding speed of 0,5 m/min has been achieved (untreated backside). Due to the variety of the effects playing a role during treatment, only structuring without pre-coating is described in this article. Relation between the plasma parameter and efficiency of the treatment process could be established. Properties of modified polymers are discussed.