By Cameron Chai
A joint project, PolAR has been initiated by the Fraunhofer FEP and the Fraunhofer IOF along with their industrial partners, including Southwall Europe, Rodenstock and Leica Microsystems, to develop an innovative, continuous roll-to-roll process for producing large-area polymer films with anti-reflective properties.
The advanced plasma-etching process improves the base roughness of the large polymer films and creates nanostructures called troughs and crests over the films. The effect of the structures is based on the moth eye principle and the nanostructuresare smaller compared to the wavelength of visible light. The structures allow continuous change of the refractive index between the external medium and the film, which leads to reduction in optical reflection of the films. For example, optical reflection of PET film is decreased from 12% to 0.2%. In addition to application for films, the plasma-etching process is also ideal for generating anti-reflective properties for curved substrates.
Fraunhofer team has made a major technological innovation by creating nanostructures on large surfaces using an efficient process. In roll-to-roll pilot facilities, such as those deployed at the Fraunhofer FEP campus, kilometer-long films with anti-reflective properties can be mass produced. Dual magnetron systems are used to deliver a stable and effective ion current for several hours. The plasma-etching process has already been successfully utilized on lacquered films, fluoropolymer films (ETFE),triacetate cellulose (TAC) films and PET films.