Fraunhofer FEP Develops New Technology for Ultra-Smooth Polymer Films

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has developed a new technology for the production of ultra-smooth polymer films as part of the OptiPerm project. This project received funding from the European Union and the Saxony State Ministry of Economics, Labor and Transport (grand agreement no. 3000651169).
 
The technology, which was previously demonstrated on samples in A4 format, has now been transferred to a roll-to-roll process with even higher surface quality. These results were presented for the first time at the AIMCAL conference in Munich, Germany in June 2018 by Dr. Steffen Günther.
 
Smooth surfaces with low defect densities are of great importance for many application areas, be they decoratively coated vehicle bodies, high-gloss and dirt-resistant furniture, or ultra-smooth metal and plastic films that serve as substrates for high-tech industries. Particularly in latter case, subsequent finishing steps can only exhibit their full potential if the surface quality of the substrate is also at a very high level.
 
For example, films for encapsulation of electronic components need thin permeation barrier layers made by a vacuum coating process that prevent against penetration of oxygen and moisture. Defects on the substrate surface would compromise these thin coatings.
 
The deposition of active electronic layers, for example for OLEDs or touch screens, requires ultra-smooth surfaces to ensure reliably capabilities such as light emission and conductivity over large-areas.
 
Scientists at Fraunhofer FEP have now developed a new method for creating ultra-smooth surfaces – dubbed the smoothing-film approach. “This innovative process does not require any special processing environment and could therefore also be used under standard factory conditions,” explained Dr. Steffen Günther, project manager at the Fraunhofer FEP. “Expensive clean rooms are not required for this process.”
 
With this new approach, a wet coating is first applied to a flexible substrate. Immediately afterwards, the coating is covered while still wet with a second film, the smoothing film. Subsequently, the wet coating is cross-linked through the smoothing film by a drying process. An electron beam is used at Fraunhofer FEP due to its high performance regarding cross-linking ratio.
 
The smoothing film may be lifted off directly after cross-linking or stay on top the coating as a protection until the next downstream processes take place. In order to reduce the costs for the smoothing films, their reusability was examined. The scientists were able to show that even after reusing the smoothing film ten times, no increase in defect density or decrease of surface quality was observed.
 
The process was initially carried out and evaluated on samples in A4 format. Subsequently is has been transferred to the roll-to-roll coating line atmoFlex 1250. The results of the process transfer to roll-to-roll technology even exceeded the expectations by far.