02/05/2005
Advances in vacuum coating raise the barrier to non-EU competition
Europe is a world leader in vacuum-coated thin film technology. The FP5 project TRANSMACH has taken the production process to even higher performance levels and opened the door to new strategic applications.
Modern packaging materials need to be designed with barrier properties that permit precise control of the migration of gases, moisture, odours, fats and other substances. At the same time, such materials are subject to severe cost pressures. Metallised plastic films, for example, introduced as a lower cost alternative to aluminium foil for protecting foodstuffs and pharmaceutical products, now account for a global consumption amounting to around 20 billion m2/year.
Keeping Europe ahead
Europe is the foremost supplier of large-area vacuum coating machines, which are not only used to produce such packaging films, but also to provide essential barrier materials for incorporation into solar cells and flexible displays for electronic equipment. This, in turn, forms the basis for a healthy EU materials conversion industry, involving a large number of the region’s SMEs.
The FP5 GROWTH project Transmach was launched in 2001, with the aim of protecting Europe’s technology lead by addressing increasingly stringent performance requirements and extending the technology to further strategic application areas.
“We faced a difficult situation,” says coordinator Professor Stergios Logothetidis, of the Aristotle University of Thessaloniki (AUTh). “EU regulations were stipulating a five-fold reduction in the gas permeability of flexible packaging films within three years, while levels needed to be even lower for emerging technical applications. At the same time, a growing demand for transparent films with well-defined optical properties necessitated research into new types of coating.”
To provide tailored barrier properties while retaining the transparency of polymer substrates such as Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN), the films are coated with vacuum-deposited oxides – of silicon or aluminium, for example – or with ceramic materials. These are applied using high-speed reel-to-reel machines running at up to 10m/s and handling web widths of 1-3 m.
Technological challenges
“Our goal was to develop a new generation of integrated and cost-effective equipment, with real-time measurement of coating parameters and intelligent automatic control of the process,” Logothetidis explains. “The challenge was to devise a means of monitoring the thickness and quality of the transparent coatings on a fast-moving and vibrating surface. Experience in an earlier project had indicated that Spectroscopic Ellipsometry (a form of optical spectroscopy based on polarized light) was the only practical option, but this needed to be developed and then transformed from a laboratory technique into an in-line industrial method.”
With help from the European Commission, a consortium was assembled that included the German machine manufacturer Applied Films and Swiss end-user Alcan Packaging Services, together with the Fraunhofer Institute for Process Engineering and Packaging (FhG-IVV), and the French optical unit and metrology producer and specialist Horiba Jobin Yvon, which had been a participant in the earlier project.”
The partners determined that very fast optical measurements using wavelengths in the visible to far UV region would be ideal for their purposes. By the end of the 39-month funding period, they had designed an on-machine system capable of performing ultra fast measurements simultaneously at 16 different and well-specified wavelengths in just 20 milliseconds! This enabled data to be collected at intervals of a few centimetres along the web length and fed back for immediate process adjustment. In addition, they had made considerable progress towards the implementation of simultaneous measurement in the transverse direction, to give a complete real-time map of coating uniformity across the whole web surface.
At the same time, the group investigated the effects of variations in the coating formulae, which they were able to test and optimise with the aid of a laboratory-scale coater at the laboratory of ‘Thin Films – Nanosystems and Nanometrology’ at AUTh and FhG-IVV, and then transfer these findings to pilot scale, reel-to-reel coaters, at Applied Films and Alcan Packaging.
Benefits for industry, end-users and the environment
“The process is extremely efficient in its use of materials,” maintains Logothetidis. “Vacuum-applied layers only ~30 nm thick can now replace aluminium foil that is 1 000 times thicker, with no reduction in the level of protection. Also, enhanced quality control will reduce process waste to a minimum.”
“Transmach has been a highly successful project from all viewpoints,” he adds “Based on the findings of this initiative, Horiba Jobin Yvon has already established a market for its ultra fast ellipsometer systems. Applied Films is in a position to build machines, incorporating the Horiba Jobin Yvon ellipsometers, tailored for the latest coatings, and will be able to retrofit on-line control to existing metallisation machines.”
For end-users, the technology brings substantial performance improvements compared with existing lacquer-coated films. As well as safeguarding the health of European citizens by extending the shelf life of foods and drugs, it is creating fresh opportunities for equipment suppliers in large-scale advanced microelectronics applications, such as the encapsulation of photovoltaic cells and organic LEDs.
An extension of this valuable work is assured with the February 2005 launch of a follow-up project called “Ultra-high barrier films for reel-to-reel encapsulation of flexible electronics” (Flexonics): a STREP under the Sixth Framework Programme. Flexonics focuses on the development of novel transparent materials systems with controlled optical properties, consisting of alternating inorganic/organic layers of a few nanometers thick. These could radically improve the current barrier properties of flexible substrates that will be used for the production of future flexible electronic devices.
Key data
- Project
- Transmach – Transparent films vacuum coatings machine with integrated in-line monitoring and control
- Key Action on Innovative Products, Processes and Organisation, FP5 GROWTH programme
Programme