PETpla.net Insider 07+08 / 2011

BOTTLE MAKING 18 PET planet insider Vol. 12 No. 07+08/11 www.petpla.net New coating technologies for beverage packages Barriers without frontiers* The Institute of Plastics Processing (IKV) at RWTH Aachen University, Germany, is currently investigating a process to improve the barrier per- formance of plasma polymer layers using a substrate bias. Here are some results of the study. Since the last developments in light weighting and barrier coatings, PET bottles have become a serious alternative even in applications in which classically glass is used. PET bottles have never been more compel- ling for beer bottling; convenient, shat- terproof, material and energy efficient. The forecasts promise an increased consumption of up to 5.3% to 7.7 bil- lion packaging units worldwide until 2015 [1]. An essential aspect in further development, in order to widen the scope of application not only for PET, but also for materials such as poly- lactide (PLA), is to enhance the low permeation barrier of plastics. For certain applications plastics in packaging do not provide a suffi- cient permeation barrier for gases. To overcome this weakness, innovative technologies have been developed. Besides the use of monolayer-blends, the plasma coating process is increas- ingly attracting attention due to its cost attractive and effective barrier enhancement. It consists of the depo- sition of a thin barrier film (20-100nm) on the surface of the bottle. This film is obtained by exciting a monomer- composed gas with microwave energy under low pressure. To meet the chal- lenges and rising demands of modern packages on excellent barrier proper- ties for a high shelf life of the pack- aged good, increasing effort is made to further enhance the performance of modern plasma coating processes. At this, not only existing processes are optimised, but new process variants and new coating systems are evalu- ated. First key experiences come from coating of plastic foils. It was discovered that a substrate bias leads to a significant increase in the bar- rier properties because the negative effect of layer defects is reduced by ion bombardment during film deposi- tion. Extensive studies on its suitabil- ity targeted at bottle coating cannot be found in literature. Interior coating of PET bot- tles using a substrate bias Within the development of a suit- able coating reactor to investigate the interior coating of PET bot- tles using a substrate bias, strong emphasis has been placed on investigations concerning different bottle shapes and materials. Fig.1 shows the plasma polymerisation reactor used for coating thin films. The design of the used microwave- induced plasma reactor consists of a stainless steel cylindrical tube using a microwave (MW) driven plasma source. Microwaves, generated from a magnetron (2kW, 2.45GHz, IBF Electronic, Ober-Ramstadt, Ger- many) are coupled into the process- ing chamber using a coaxial wave- guide system which is arranged in the lid. Under certain circumstances, including the overall gas flow into the chamber, the amount of micro- wave energy and pressure condition (2-100 Pa), the microwaves create and maintain a low pressure plasma. The reactor used is of in-plasma type i.e. the substrate to be coated is inside the plasma volume. There- for the vacuum chamber contains a socket to hold the sample. Other periphery like vacuum pumps, a pressure controller and four gas flow controllers correspond to the standard design. In order to excite a plasma and deposit a coat- ing on the interior of the bottle the upper antenna is used to conduct the pulsed microwave energy into the chamber, while the isolated hollow Figure 1: Plasma reactor for substrate biased coating of bottles sensitive BEVERAGES