No barrier to progress - new melamine barrier coating
With the global packaging market increasingly seeking more environmentally responsible solutions, a new melamine-based coating offers potential benefits.
The packaging market is changing dramatically in the face of an escalating global focus on sustainability and waste management. Barrier-coated flexible packaging – both metallised and clear – is a much-favoured choice today among brand owners and retailers around the world (as also referred to in this issue in Euromonitor’s overview of the Indian market). It offers consumer convenience in terms of reduced weight compared to most rigid packaging, and ease of handling – particularly for liquids and foods.
According to Pira International, barriercoated packaging is forecast to grow at 4.6% annually to 2014, with food and beverage identified not only as today’s largest market sector, but also as one of the markets with the best development prospects.
Flexible packaging and aseptic containers are increasingly replacing traditional technologies such as multi-layer bottles and metal cans. This movement is a result not only of the desire to find less energy-intensive solutions to packaging, but also because, in many cases, it has become very difficult to further reduce the thickness of metal and glass containers without compromising effective performance.
There are several barrier coating options available today, including aluminium oxide, silicon oxide, carbon and epoxy, as well as melamine-based Freshure. The latter, employing proprietary Symphase technology developed by the Netherlandsbased science company DSM and licensed by its Knowfort Technologies BV subsidiary, has been identified in a recent Pira International study as having the potential to ‘bring a major breakthrough in transparent polymer barrier films for food and pharmaceutical packaging’. Freshure coatings have enjoyed strong interest around the world in the three years since they were launched.
Freshure coatings certainly tick a number of boxes in a packaging buyer’s wish list for barrier coatings today. They offer effective barrier properties at a low cost for flexible packaging applications, delivering a transparent, impermeable coating via the vapour deposition of melamine on clear or metallised substrates. Melamine is inexpensive, environmentally sound, fully recyclable, biodegradable and approved by the US Food and Drug Administration for food contact. In addition, unlike many raw materials today, it is in plentiful supply.
These melamine-based coatings can be deposited in one of two ways, depending on the application. To deliver a functional, transparent gas barrier only, a Freshure- Single Coat can be used. Alternatively, to improve surface tension and add barrier functionality, a Freshure-Top Coat can be applied in conjunction with a barrier of aluminium or aluminium oxide.
The Symphase vacuum production process, which uses supramolecular chemistry, is flexible and uses relatively little energy, making it suitable for sustainable manufacturing. Under moderate vacuum conditions and above its low sublimation temperature of 200°C, melamine can cover a large surface area in a fraction of a second, creating a layer of transparent crystalline coating, less than 100 nanometres thick, with high gas barrier properties.
This image shows a scanning electron microscope image of a vacuum applied melamine coating –
The coating is added at moderate temperature (~300°C) and vacuum (~10-2mbar) at speeds up to 9m/s. This table indicates the oxygen barrier properties of Freshure- Single Coat –
It shows the oxygen transmission rates of melamine coated onto various polymeric substrates. The performance of Freshure is comparable to that of oxide coatings, and better than ethylene vinyl alcohol and polyvinylidene chloride-based alternatives.
This chart shows the barrier properties of a series of metallised and oxide-coated films with and without Freshure-Top Coat –
The chart also shows the significant barrier effect it has on both oxygen and water.
Conversion of metallised films with Freshure coatings to packaging containers is less complex than with many (metallised) films. There is no need for in-line corona treatment prior to conversion, and Freshure-Top Coat is instantly printable, with no reduction in metallic gloss levels. For many applications, this can be a key feature – other metallised films often require the off-line application of print primers prior to printing to deliver good aesthetics. This adds an extra process, and can also damage the oxide/metallised layer.
Melamine-based coatings are less brittle than inorganic coatings, and do not fail at high temperature or humidity. They can extend the shelf life of metallised films from the standard 60 days to six to 12 months and even longer, adding real value for the converter of flexible packaging films.
Applied Materials Inc, a global roll-to-roll coatings specialist that offers a wide range of vacuum web coaters for a variety of applications, including packaging metallisation and flexible electronics, has, in collaboration with DSM-Knowfort, developed a high-volume manufacturing capability for Freshure. The versatile web coater platform applies transparent barrier layers, while delivering higher productivity than standard vacuum coaters, with resultant reductions in production costs and global technical support.
Symphase technology has been successfully employed on Applied Materials’ industry-proven TopMet Clear vacuum metallising equipment, delivering an effective and flexible ‘package’. This system enables metallisation on a wide range of substrates, including biodegradable films and oriented polypropylene, with the application of additional barrier layers. The equipment can, for example, apply Freshure Single Coat on plastic films for improved barrier properties, aluminium metallisation with Top Coat for barrier properties and improved consistency of surface tension, or deliver a combination of aluminium oxide clear barrier – an inorganic layer that offers barrier properties and improved mechanical stability – with Freshure Top Coat for optimal barrier performance.
In the food and beverage market, barriercoated flexible packaging is particularly favoured. However, this technology is likely to be adopted in other segments of the packaging market, since it is environmentally benign, and unhampered by the cost pressures of metallising.
Markets where protection of the product is a central concern could be quick adopters – particularly pharmaceuticals and medical disposables. Additionally, as liquids and beverages move increasingly from glass to barrier-coated PET bottles, further opportunities are being explored in both multi- and mono PET bottles, where they can offer improved aesthetics over alternative barrier coatings, with the added benefit of full recyclability.