Aluminium Oxide transparent barrier coatings

Aluminium has long been the main vacuum coated barrier material but it does, of course, have the property of being opaque. So for those wanting a transparent barrier coating they have always looked to other materials of which the most popular has been some version of silica.  Most time this is a sub-stoichiometric version of the silica and in the case fo the plasma enhanced chemical vapour deposition (PECVD) process it also contains an amount of carbon, anywhere up to 20%, or more, depending on process conditions.

The cost of these alternative materials has been high with the lowest still being of the order 2x to 3x the cost of aluminium metallizing.  This is because of two significant costs, the capital cost of either a PECVD or an electron beam deposition system is a much higher cost than a resistance heated boat type metallizer and the deposition speed is often less than a half that of aluminium metallizing.

The one company that appeared to have solved this problem was Camvac who managed to produce an aluminium oxide coating from their modified standard metallizer.  It would appear that by them carefully introducing the oxygen at the right point and in the right quantity they could control the oxidation fo the coating but also not damage their resistance heated boats. 

Needless to say this technology has been patented and so for many years this has been the only low cost process that I have known to be operating.  However in recent times I have heard that there have been two others who have managed to develop a similar process. One I know has been checked out to make sure it was not infringing any patents and that they were clear to run production the other I do not know if it has been checked out but they are prepared to talk about the process and will be giving a paper on the process at the 2009 SVC conference in Santa Clara.  This process was developed by the Fraunhofer Institute in Dresden (FEP) in conjunction with a polypropylene converter and the Applied Materials built a machine using the technology for use in production.  The FEP specialise in using additional plasmas during deposition to activate any reactive gases and to also promote surface reactions and densification of the growing coating.  Thus I expect that this process uses that expertise to evaporate the aluminium quickly but then use the plasma to activate the oxygen to speed up the conversion of the metal to the oxide.

As aluminium oxide is less dense than the metal this conversion from metal to oxide can also help improve the barrier as it will add a compressive component to the coating, as it swells, that will close pores down and make diffusion through grain boundaries slightly harder.  If this technology is now available through one of the system builders then this could mean that the cost of obtaining transparent barriers could be due for a fall in the next couple of years as these coatings start to become available.

Comments

[Andrew Mitchell]

Ultimet Films Limited have own Aluminium Oxide coated barrier film process which they have developed over a period of 6 years which is currently running production film at processing widths of 2.0 metres+

The Fraunhofer process has been around for many years and papers describing this process were published as long ago as 1996. The Fraunhofer system was finally incorporated into an Applied Films machine that was supplied into a BOPP producer based in Columbia early this year and this machine also incorporated the DSM Melamine coating process which allows this BOPP supplier to produce either Melamine Coated Films, AlOx coated films or AlOx coated films top coated with Melamine.
As the Fraunhofer system been utilised in a new machine at a film producer there has been a push to promote the technology again at various conferences.