Nanotechnology is being applied to improve the gas barrier properties of coatings. In doing so, nanoclay is dispersed in barrier coatings, resulting in a platelet orientation that creates a “torturous path” for gas molecules to traverse, yielding a very thin film, effective gas barrier.
Traditional Barrier Materials for Food Packaging
Traditionally, tinplated steel, glass and aluminum have provided the ultimate in oxygen O² and moisture MVTR barrier materials for food packaging. These packaging materials offer zero gas, and vapor transmission rates. Glass, of course, has the added benefit of being transparent.
Environmental Concerns Provide Continuous Improvement in Packaging Materials
Recycling, environmental friendliness and sustainability have become issues for all packaging, providing the opportunity for new packaging materials development. As a result, continual improvements in polymer films, surface treatments, and coatings are yielding new packaging alternatives while respecting environmental impact.
Single or multilayer plastic films generally lack the ability to provide an optimum gas barrier. The addition of aluminum foil lamination is an industry standard offering an optimum gas and MVTR barrier; however these are expensive and not transparent.
Metallized aluminum and transparent oxide coated plastic films provide useable O² and MVTR performance. Inorganic AlOx and SiOx oxides deposited by electron sputtering are not cost effective. However, AlOx and SiOx metallized by vapor deposition to films is cost effective. SiOx and AlOx coatings are commonly used on PET and BON films.
Unfortunately, these coatings are not heat sealable so they are used in multilayer film constructions sandwiching the damage susceptible oxide film between plastic film layers. Oxide film depositions on films may also be protectively in-line coated using sol-gel materials.
The global growth of these inorganic transparent barrier films is forecast to grow at high rates even with their gas and MVTR limitations compared to aluminum foil. They are attractive for stand-up pouch applications, meat pack lidding, microwavable, retort and dry food packaging.
Commonly used plastic packaging films based on polyethylene terephthalate PET, biaxially oriented polypropylene BOPP, biaxially oriented nylon BON/OPA, polyactic acid PLA, and cellulose MXXT/W, MS lack in the gas barrier properties required for long shelf life food packaging.
Seeking to overcome these deficiencies a variety of coatings have been developed. These have, with a variation of results, improved gas barrier properties, as well as offered heat seal capabilities, product resistant properties, transparency, and gloss.
These coatings include both organic solvent and aqueous polyvinylidene chloride PVDC, aqueous polyvinyl alcohol PVOH, aqueous, and extrusion coated ethylene vinyl alcohol EVOH, and organic and inorganic sol-gels. Each of these exhibits desired performance limitations of one sort or another.