By Melissa Donovan
Packaging is a growing segment of digital print. While today’s ink sets offer a certain level of durability, coatings provide a higher level of protection that packaging requires because it is handled so frequently. Besides durability benefits, coatings also provide a different aesthetic—creating a gloss or spot coat. In these instances coatings are typically applied after the print and considerer overcoatings. Coatings or primers can also be applied prior to printing. These also provide a host of benefits from enhanced adhesion to speeding up processing times.
In either the pre- or post-coat scenario, it’s important to pair the correct coating—UV or aqueous for example—with the appropriate ink and substrate. Furthermore, there should be a discussion about whether the packaging is involved in food or beverage, then the coating needs to be vetted based on a number of certifications.
Coatings provide a number of benefits. Specifically in the industrial sector, referring to manufacturers digitally printing packaging, some of the most influential benefits include improving ink adhesion to the substrate, enhancing the look and feel of the graphic, and even making it easier to fill a package—all while protecting the printed product.
According to Terry Amerine, VP – sales and marketing, Polymeric Group, industrial/packaging segment require-ments are typically more challenging. “Coatings are designed to enable the ink and end product to meet certain requirements. It could be the need for greater adhesion or less migration; texture, finish, and feel are other popu-lar attributes coatings can provide.”
Prior to print, coatings or primers provide numerous features that packages benefit from. “Ink receptive coatings provide a surface that can enhance the adhesion of the inks to the substrate, seal uneven surfaces to improve print quality and appearance, and bond or react with the inks to improve durability and allow faster processing times,” explains Shannon Cook, business manager, tapes, labels, and coatings business, H.B. Fuller Company.
A number of substrates present adhesion challenges. “Ink receptive coatings provide the choice of printing on standard substrates such as clay coated offset stock without sacrificing print quality and provide good ink adhesion to difficult substrates for bonding between liquid toner and flexible packaging substrates,” says Susan Bailey, business development manager, digital and specialty printing, printing and packaging, Michelman.
Corrugate board is porous, so ink inherently wants to seep in. Without a coating, too much ink is absorbed in the board. This negatively impacts the brightness and image quality, shares Kelly Lawrence, global market segment manager, innovation, The Lubrizol Corporation, A Berkshire Hathaway Company. “Ink receptive coatings play a role in reducing total cost to print. Primer holds the ink on the surface of the corrugated packaging so less ink is required to achieve the desired optical density,” continues Lawrence.
A bit out of the traditional packaging realm, but a container, ink receptive coatings are also helpful when printing on glass. “Primer enhances the durability of printed UV inkjet inks on glass with regards to scratch resistance and water fastness,” adds Stefan Fiedler, IRIS GLASPRIMER, Stefan Fiedler Imaging GmbH.
Post print, protective and enhancement coatings extend shelf appeal. John P. Vogel, president, Chesapeake Digital Consultants, a consultant for Alliance Technology Corporation, provides examples of specialty coatings like soft touch, grit, and glitter in high gloss or matte.
“By enhancing the aesthetics of the package, coatings can be used to better catch the eye of the consumer as the package sits on the shelf. Adding a variety of special effect coatings to packaging can create a sensory effect that goes a long way toward grabbing the attention of consumers. Items such as glitter, pearl, or metallic coatings, combined with contrasting matte and gloss effects provide stimulation and differentiation,” recommends Phil Jackman, global product manager – digital, Sun Chemical Corporation.
An additional benefit of a post coating or overcoating, depending on the type, it can aid in the converting, filling, and shipping of the package. “Coatings that change the slip or coefficient of friction of the surface of the package allow for freer movement through and around the processing equipment, enabling increased line speeds. Heat- and cold-seal coatings can help in the sealing and closing of the package; again, increasing line speeds. The co-efficient of friction of the surface of the package can also increase, allowing packages to be better and more stable when stacked,” admits Jackman.
Vogel points out though, that, “all of this is dependent on the digital ink used, end use of products, and the substrate being printed. No one answer applies to all.”
Extending Color Gamut
Drilling down deeper into specific benefits, coatings extend color gamut. While in analog printing, color is applied via plates, offset rolls, or screens, this limits the number of colors printed or the color gamut. In digital printing color gamut is greatly increased compared to traditional analog practices. Coatings extend the color gamut even further, allowing printers to meet brand owners’ color-critical requests.
“In digital printing, color match is done through an electronic profile that tells the printhead exactly what size and mix of ink droplets to jet. Color gamut is increased to include any color combination of the ink droplets. Color is perceived by how the eye reads the dots on the substrate. If the dots vary in size and shape or if the ink sinks into the substrate, the color—or how color is perceived—is affected. Primers or coatings help control dot spread and keep ink on the surface, which further optimizes the color gamut,” explains Lawrence.
“Ink receptive coatings extend the color gamut because the ink colorant remains at the surface of the substrate through chemical and physical interactions,” adds Bailey.
Thanks to a combination of coatings and digital print, packaging is being transformed. “Digital printing offers packaging printers the benefit and capability of high-quality color reproduction, which helps create packaging that engages and connects with consumers. It enables a broader range of imaging, including high-gamut sensitive corporate logos,” suggests Bailey.
Coatings also help digitally printed pieces match analog printed pieces. “Consumer packaged goods marketers spend a lot of time and money on brand standards and expect their colors to match across packaging types and promotional materials. When a printed mock up is shown to a client, the finished piece must match exactly,” adheres Lawrence.
Vogel explains that printers are either moving existing analog printed products to digital or printing large-sized packaging analog and smaller sized packaging on digital. To get the two to match, digital presses may require an inline primer coating or previously applied coating to provide the proper surface for the best print.
A second important benefit of using a coating is it enhances durability of the package. It’s important to create a product that can withstand human touch while maintaining its shape moving through the printing process and between processing facilities, to a transportation vehicle, and finally out on presumably a store floor.
“Many digital inks lack the post-print durability required for either the customer fulfillment process or the stress of transportation of the finished product. Standard protective coatings are provided with names like high rub, high slip, or low slip,” explains Vogel.
Amerine shares that inks used in packaging have a high degree of flexibility, so they tend to be softer and more prone to scratching and damage in handling. “As a result, the coatings provide more durability to the underlying ink.”
Additives to the coatings like resins provide other features and benefits. For example, Vogel points to a package that may require a specific slip or slide angle so that the packaging does not slip while being moved from printer, but still provides the necessary slip and runability for production lines and transport of the finished product.
“Ink receptive coatings offer packaging increased functionality as well as aesthetic performance. Coatings broaden the versatility and increase the robustness of packaging by providing water, vapor, oil, and grease resistance,” shares Bailey.
Coatings not only protect the contents of the package from the environment, but the package from its contents. According to Jackman, the primary purpose of any package is to protect its contents. “Barrier coatings help prevent oxygen and moisture from migrating through the package. Conversely, there are coatings that keep moisture, oil, and grease from the products being packaged from damaging the package. These barrier coatings—used correctly in the design of the package—can greatly increase the shelf life or usability of the product.”
Barrier coatings serve a second benefit. “By using a coating in place of more substrate, coatings provide significant light weighting or down gauging of the package by using less total material mass to do the same job,” adds Jackman.
Packaging is prevalent in the food and beverage market. When it comes to food safety and other health and even environmental concerns, there are a lot of factors to take into account when suggesting a solution for a digitally printed package.
Jackman says it is worth mentioning that formulation ingredients are cleared by the FDA for use in food packaging but not approved. “One of the main priorities for brand owners, converters, and customers is compliance and the issue of migration. Low migration and compliance are also important factors in digital printing and if not handled correctly, could have potentially severe consequences, such as damage to a brand’s reputation and risks to consumer health.”
“Currently there are some aqueous coatings available in the U.S. for direct food contact that are FDA compliant, but not approved. They are available from several suppliers. With proper barriers in packaging, many coatings including UV can be used. Some packages require low odor and/or low migration,” adds Vogel.
Coating vendors have several practices in place to address the constantly evolving health, safety, and sustainability standards.
Coatings are instrumental in achieving the ideal digitally printed package. Prior to print, primers or pre-coats offer advanced adhesion between the ink and substrate, while simultaneously expanding the color gamut. Post print, overcoatings provide durability so the printed package avoids damage during processing, handling, and shipping. They also maintain appearance while the package is in its final environment—prolonging shelf life and protecting what is inside the package.
Aesthetically, coatings serve as a visual enhancement, achieving gloss, matte, glitter, and other specialty looks for a package to standout on a crowded shelf.
Coating vendors stay abreast of continuing changes in environmental and health safety regulations as more digitally printed packages enter the food and beverage industry. The right combination of ink, coating, and substrate enables digital printing technologies to further penetrate the highly lucrative packaging market.
Sep2019, Industrial Print Magazine