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Flexo Sustainable : Spring 2013
rier coating. In Figure 3, a coated film, PVdC coated PET is replaced with a barrier coated corona treated PET. The film is then laminated in the usual way to a sealant web of polyethylene. The benefits of this new structure are an im- proved oxygen barrier of up to 10 times the previous structure without chlorine and longer shelf life. Another example, (Figure 4), is the Oxygen barrier enhancement example of a commercial three-ply laminate to a new three-ply laminate plus printable barrier coating by providing lower cost than alter- native high performance barriers. PRACTICAL CONCERNS Application weight of barrier coat- ings is critical to obtaining high barrier numbers. Depending on the substrate, application weights need to be ad- justed to attain the barriers desired. In Figure 5, the relationship between application weight and oxygen perfor- mance is detailed. Anilox and gravure suppliers can offer advice on the best screen and line combinations for the deposition weights desired. The nano clay coatings are often supplied in two or more parts that need to be mixed together before use. An air-powered mixer press-side is usu- ally adequate to mix the components before use. Newer versions are available as a one-part system and should be kept from freezing. Corona treat films before coating, as it will enhance adhesion and improve lamination bond strength. Substrates should be free of dirt and dust as much as possible and should be applied as the first down with inks and other materials applied as a sec- ond down. The oxygen transmission rates of typi- cal flexible packaging materials can be drastically improved by printed oxygen barrier coatings and provide a viable al- ternative to existing film options. Figure 6 provides gas barrier performance across multiple substrates on polyester, oriented polypropylene and OPA at room temperature and relative humidity. Nanocomposite coatings provide excel- lent barrier performance on both PET and OPP with dry film weights as low as .2 g/m2 (dry). Gas barrier coatings also provide improvements in flexibility and lamination integrity. Values of oxygen barrier coatings include: excellent oxygen and aroma barrier, the replacement of PVdC and EVOH coatings, improved flex crack resistance of oxide/metallized films, and extended shelf life. Application of high oxygen barrier coatings can take place: • At conventional film weights, depending on the structure and barrier required • On existing equipment • Through the removal of barrier film and adhesive in three-ply and more laminates Figure 2: Various coatings on typical packaging films show they were subjected to a Gelbo flex tester to measure oxygen barrier before and after flexing. Figure 3: A coated film, PVdC coated PET is replaced with a barrier coated corona treated PET. The film is laminated to a sealant web of polyethylene. Benefits of this new structure are an improved oxygen barrier of up to 10 times the previous structure without chlorine and longer shelf life. Figure 4: Oxygen barrier enhancement of a commercial three-ply laminate to a new three-ply laminate plus printable barrier coating provides lower cost than alternative high performance barriers. www.flexomag.com sPrinG 2013 Sustainable FLEXO 7
Earth Day 2013