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FLEXO Magazine : Sustainable Spring 2011
Sustainable Solutions for Barrier Packaging By Peter Brownrigg The packaging market’s need for products that deliver enhanced shelf life, as well as sustainable, recyclable, metal-free and waste reducing solutions can be ad- dressed through a revolutionary approach that replaces cur- rent barrier technology with printable barrier coatings. Traditional structures of glass, tin and foil are often seen as formidable barriers but, like all barrier technologies, have their disadvantages. Weight is considered a limiting factor for these substrates. While coated plastics offer barrier improvements, overall plastics provide a poor barrier and there are downsides, such as the generation of chlorine from PVdC, the presence of metal in metalized film, the thickness of extruded laminates, and the fragile nature of AlOx and SiOx coated films. New emerging technologies, such as nano composites, can now be used to offset such deficiencies, and these technologies can be formulated into functional coatings suitable for print- ing on packaging. The food packaging market needs are quite broad and include: • Chlorine-free structures. • Alternatives to other more expensive barrier technolo- gies. • Excellent O2 /Gas/ aroma / odor barrier. • Barrier to other potential migratable compounds. • Extension of shelf life. • Lightweight materials. • Sustainability. • Reduced carbon footprint. • Replacement of structures, containing metalized film. • Recyclability. • Transparency. • Improved flex crack resistance when compared to oxide / metalized films. • Waste reduction. DESIGN & FORMULATION Barrier coatings that can be applied at conventional print- ing converting wet film weights are difficult to formulate. Sig- nificant improvement to gas barrier, as illustrated in Figure.1 , can be obtained by dispersing or exfoliating mineral silicates in the organic polymers selected for coatings. In this category, clays provide the most significant improvements due to their “platy ” structure. There are many types of clay which vary in crystal structure and “platiness” . These minerals are very thin (about 1-3 nanometers) and, when correctly exfoliated in a coating, they align parallel to the substrate. Each platelet is an absolute barrier to oxygen, so getting them all to connect would provide an excellent barrier. In reality, this can’t be achieved but, when optimized , 10 Sustainable FLEXO SPRING 2011 www.flexography.org