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COATINGS EXPLAINED
Coatings can extend the look and life of your package. How to pick the right one.
They're about the thickness of a human hair and you usually can't see them. But coatings are one of the most important components of your packaging.
Why are coatings so important? For some of the same reasons that packaging is important. While packaging protects and enhances the beauty of what's inside, coatings help protect and enhance the appearance of the package itself. Because coatings are dually decorative and protective, they are an economical way to extend both the appearance and the lifespan of the package.
One of the goals of packaging is to catch the consumer's eye, encouraging them to examine and explore the package and its contents. A quality coating increases shelf appeal by adding snap to printed graphics and imparting additional tactile elements. Designers can also use the wide range of coating finishes available—from matte through satin to gloss—to create new packaging design options to attract consumers.
A coating also protects the package from the rigors of assembly, fulfillment, shipping and distribution, safeguarding it from abrasion and scuffing. In some cases, coatings can even eliminate the need for shrinkwrapping or other protective layers.
The most common types of coatings used today are Ultraviolet (UV) and aqueous. Both are available in a range of finishes and both demonstrate excellent abrasion and block resistance.
Which is the best coating for a job? That depends as much on the job as it does on the coating. Expectations of performance, appearance, quality and cost are variables to weigh when making a decision. Other factors to consider include supplier experience, job latitude (tolerance), storage conditions and performance requirements.
We'll begin with a comparison of UV and aqueous coatings, and then discuss the most appropriate applications of each. Finally, we'll take a brief look at one of the newest coating technologies, electron-beam (EB) coatings.
Aqueous coatings are approximately 60% water and 40% solids. During the drying process, the liquids evaporate or are absorbed by the substrate, leaving the solids to form a thin film. Aqueous coatings are clear and odorless when dried, and are also available in FDA-approved formulations for use in food packaging.
UV coatings are 100% solids, and finish by light-curing rather than heat-drying. The solids cross link to form a durable plastic film that provides unparalleled gloss and hardness. UV offers a broader range of finishes than aqueous, including options such as metallized flakes or pearlized pigments. Although UV coating can be applied either in-line or off-line, in-line UV coating offers comparable finish quality plus the advantages of increased speed and reduced cost compared to the off-line UV coating process.
Both UV and aqueous coatings offer the convenience of in-line application and rapid drying, allowing for instant work and turn. In fact, either type of coating can be used with little or no spray powder, improving surface smoothness and creating a cleaner work environment. In addition, both coatings can be applied as an overall or "flood coating", or as a spot covering to highlight a particular image or area.
Aqueous coatings generally cost less up front, but the quality advantages and productivity gains of a UV coating often outweigh the higher unit costs. When comparing costs it's helpful to think of UV as conferring all of the benefits of aqueous coating, but to a greater degree. For example:
• Aqueous dries fast — UV dries faster
• Aqueous can be glossy — UV is glossier
• Aqueous provides protection — UV provides more protection
Another difference between aqueous and UV coatings affects their use in food packaging. Unlike aqueous coatings, UV coatings (and inks) cannot achieve a 100% cure. As a result, there is a risk that some of the material from a UV coating could migrate into a food product with which it has contact. As a result, the FDA has not approved UV coatings for direct food contact.
Appropriate applications for aqueous coatings include:
• Food packaging (for direct food contact)
• In-line heat seal blister packaging
• Primer / seal coating (to enhance gluing or subsequent UV varnish over conventional inks)
• Items that will be written on (e.g. mailers, postcards, etc.)
• Smaller jobs in which cost is a major issue
UV coatings are particularly well suited for:
• Applications requiring the ultimate in gloss
• Applications requiring the ultimate in hardness
• Non-absorbent print surfaces (e.g. plastic, Tyvek ®, etc.)
• POS displays
• Spot coating
One of the newest coating technologies being applied to packaging, electron-beam (EB) coatings, provides the gloss and hardness benefits of UV coating while allowing for direct food contact. EB coatings achieve this through a similar formulation as UV coatings, but a unique curing process. Rather than using ultraviolet light to cure, EB coatings are cured instantly and completely with an electron beam. As a result, EB coatings have broad applications, from food packaging, to packaging requiring high gloss or hardness, to spot coating. However, the benefits of EB coating must be traded off against the costs of a new technology. EB coatings are currently more expensive than their UV or aqueous counterparts.
Choosing a coating is an investment in the lifespan and performance of your package and, ultimately, the product inside. For help in understanding coating options and choosing the best coating for your packaging, contact an ICG company. A list of ICG companies can be found at http://independentcartongroup.com/members.htm.
Dennis Bacchetta from ICG member Diamond Packaging contributed this article
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