Atomic Layer Deposition Process for Barrier Applications of Flexible Packaging

摘要

Atomic layer deposition (ALD) is a process where thin films of material are deposited in a controlled manner one atomic layer at a time. The main advantages of ALD are the extreme degree of conformality and uniformity which can be obtained regardless of the orientation or shape of the substrate; there are no pinholes in the film. The ability to do roll-to-roll coating would open huge possibilities for the technique, because barrier layers are required to avoid the diffusion of water or oxygen through polymer or paper webs for example in the food packaging industry. According to barrier test results, the aluminum oxide coating provided by the ALD batch process improved the oxygen and water vapor barrier as a function of coating thickness by a large amount. As an oxygen barrier, a thin 10 nm coating is already able to obtain ten times lower transmission levels than the uncoated structure. As a water vapor barrier, the thickness of the polymer layer becomes practically meaningless once the thickness of the ALD-layer increases above 40 nm. With over 100 nm thickness, the water vapor transmission rates of the structures were reduced below the level of 1 g/m~2/24h (23°C, 50% RH). These results encourage the continuation of investigations towards roll-to-roll solutions of ALD processing.