Roll-to-roll technology on pilot scale for transparent ultra-high multilayer barriers
Thin transparent layers on polymer webs are used to drastically enhance the permeation barrier properties while at the same time maintaining the flexibility and optical transparency of the polymer substrates. Applications range from food packaging films to encapsulation films for solar cells or flexible electronics. Very low water vapor and oxygen transmission rates are required for the encapsulation of flexible organic solar cells and OLEDs. This paper introduces a technology for manufacturing ultra-high permeation barrier films using roll-to-roll coating processes. It is based on a multilayer approach consisting of reactively sputtered oxide barrier layers and an interlayer of inorganic-organic hybrid polymers (ORMOCER®s). The multilayer barrier is compared to other high barrier technologies and evaluated regarding barrier performance, optical transparency, surface roughness and productivity. The water vapor transmission rate (WVTR) has been measured using different methods suited for different sample sizes and test conditions. The measurement limit of a MOCON Aquatran® system (5·10-4 g/(m²d)) has been reached with a three layer stack at 38°C /90% relative humidity. The technology is now being used for a pilot production of barrier films. In addition to the barrier layers, further layers can be applied to the polymer film, e.g. layers to provide a mechanical protection, a smoothing layer for further processing or transparent conductive layers for manufacturing of flexible organic solar cells or flexible OLEDs. Different applications e.g. using the barrier film either as a substrate for organic electronic devices or for the encapsulation of such devices will be discussed.