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FLEXO Magazine : June 2013
Technologies & Techniques High Oxygen Barrier Coatings eliminating the laminated structure By Bob o’Boyle Printers engaged in the high oxygen barrier coatings market need options that are chlorine-free, enable light weighting, improve sustainability and the ability to recycle, remove metal, are transparent, and offer an alterna- tive to expensive barrier films. Since the 1990s, nanoparticulates have shown promise in coating formulations and recently have shown exciting properties when made into barrier formulations. In packag- ing applications, they most notably improve barrier to gases, aroma and UV light. Early problems with instabilities and poor coverage have been for the most part eliminated with im- proved formulations and press techniques. Functional oxygen barriers of less than .006 cm3/100 inch2 over 24 hours at 23° C and 50 percent RH on polyester are now routine. What are nanoparticles? Nano is a prefix meaning “dwarf ” in Greek; it also means one billionth. A nanometer is therefore one billionth of a meter. To provide a sense of scale, a tennis ball would be 100,000 ,000 nm. In practice, nanoparticles are finely dispersed nanoparticulate (intercalated/exfoliated) silicate mineral in a polymer solution/dispersion. As the nanoparticulates stack and arrange themselves on a flexible film substrate, they provide an obstacle to gases though the formation of a “tortuous path.” As seen in Figure 1, nanoparticulates move from agglom- erated clay to nanocomposite (exfoliated) coatings. As long as the distance d2 is greater than d1, a tortuous path exists and oxygen barrier performance is improved over an unmodi- fied polymer matrix. The uses for oxygen barrier coatings in the packaging industry are both economic and performance related. The barrier performance of these nanocomposite barriers are much improved over typical PVdC and EVOH barrier resins typically used in packaging films. While most commercial activity today is in the area of dry foods, prototypes have been made for liquid packaging, as well as chilled packaging. Ap- VALUABLE & VIABLE • Uses for oxygen barrier coatings in the packaging industry are both economic and performance related • Most commercial activity is in dry foods, but prototypes have been made for liquid packaging as well as chilled packaging • Early problems with instabilities and poor coverage have been for the most part eliminated with improved formulations and press techniques • Oxygen transmission rates of typical flexible packaging materials can be drastically improved by printed oxygen barrier coatings and provide a viable alternative to existing film options • Values of oxygen barrier coatings include: excellent oxygen and aroma blockades, replacement of PVdC and EVOH coatings, improved flex crack resistance of oxide/metallized films and extended shelf life Figure 1: nanoparticulates move from agglomerated clay to nanocomposite (exfoliated) coatings. As long as the distance d2 is greater than d1, a tortuous path exists and oxygen barrier performance is improved over an unmodified polymer matrix. 102 FLeXO June 2013 www.flexography.org