Internal and external coatings combined to create super barrier.

Researchers at the IKV in Aachen, Germany, are examining new ways to boost the barrier performance of PET bottles. By placing plasma coatings on both the inside and outside surfaces of the bottle, they are achieving considerable increases in barrier properties.

The use of plasma coatings on PET bottles is now well established and has been commercialised by companies such as Sidel and SIG. However, existing processes only apply the coating to one surface of the bottle, typically the inside where risk of damage is lower.

The IKV presented results of its initial test results at the Antec conference in Cincinnati, US, this week. These showed that the barrier performance achieved by coating both surfaces was considerably better than expected. For example, coating only the inside surface gave a five-fold increase in CO2 barrier properties, while treating the outside of the bottle only led to a four-fold improvement. However, applying a plasma coating to both the inside and outside of the bottle produced a 16-fold improvement. Researchers at the IKV have looked for reasons why the combined performance is better than the cumulative effect of each individual coating.

They believe that some CO2 molecules pass through tiny defects in the coating layer. In a single coating structure, they are then able to pass through the PET and out the other side. However, in a double coated structure, they can only complete their journey through the bottle wall if they find another defect in the coating on the other side of the PET. The chances of such flaws being in alignment is relatively small, hence the large increase in barrier performance.

The test bottles produced at the IKV so far have been produced in a two step coating process. Based on their encouraging test results, the researchers are now looking at developing a process for applying both the internal and external coatings in a single step.

Latest innovations in enhanced barrier PET container technology and markets will be discussed at EPN’s Barrier PET Bottles 2007 conference in Brussels, Belgium, later this month