Gas barrier coatings for packaging and flexible electronics

Permeation barrier films as key enabling technology. Permeation barrier films are materials that prevent transport of gases such as oxygen, water vapour and carbon dioxide through the film with the aim to control the atmospheric condition on one side of the system. Applications include e.g. packaging films for food and pharmaceutical products, thermal vacuum insulation panels in building facades, and encapsulation materials for flexible electronic devices. Performance of gas barriers is usually compared by measuring a gas transmission rate. The oxygen transmission rate (OTR) and water vapour transmission rate (WVTR) are of particular interest in the majority of applications. WVTR requirements of different products range from 1 g/(m2d) in food packaging to 10-6 g/(m2d) for organic light emitting diodes. It is important to mention that the gas transmission rate is not a material constant but depends on the atmospheric conditions (temperature, gas concentration; for water vapour: relative humidity). Higher temperature usually results in higher gas transmission rates; higher relative humidity on the «humid side» of the barrier film usually causes a higher WVTR as well, because the gradient to the «dry side» of the film is higher. Four common measurement conditions are used to determine the water vapour transmission rate of a barrier film: ambient condition: 23°C and 50% relative humidity (r.h.); tropical condition: 38°C and 90% r.h.; accelerated testing: 60°C and 90% r.h. and the damp-heat test: 85°C / 85% r.h. The damp heat test is mainly used to evaluate materials for photovoltaic modules and for automotive applications. Oxygen transmission rates (OTR) are typically measured at ambient temperature in a dry air atmosphere (23°C / 0% r.h.)