By Olivia Cahoon
Packaging manufacturers use coatings to enhance a product’s aesthetic and provide an extra layer of protection. By using a coating, packaging products remain durable and appealing during converting, filling, and shipping to deliver a polished display for shelving units.
Before selecting a coating, it’s important that manufacturers consider if it is compatible with the intended substrates and inks and if the coating will be used for food packaging. If intended for food packaging, the coating should be water-based and FDA compliant.
Form and Function
Packaging applications with an applied coating stand out on shelves even after repeated handling by customers. With an enhanced appearance, coated packaging applications capture the customer’s attention and increase purchasing likelihood.
“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,” says Robert O’Boyle, product manager, coatings, Sun Chemical Corporation. By enhancing the packaging’s appearance, coatings catch the consumer’s eye and increase shelf appeal.
Special effect coatings include features like glitter, metallic, or pearl combined with contrasting matte or gloss effects. However, coating enhancements are not limited to visual effects. According to O’Boyle, other sensory enhancements include scent, sound, texture, and function of opening the packaging.
While coatings provide a visual and tactile effect to engage customers’ senses, they also offer production efficiencies, protection, and functional benefits. John V. Vogel, digital consultant, Alliance Technology Corporation, believes that graphic designers seek more than just the package’s visual attraction and also look at its manufacture, durability, and functions. “Coatings play a key role in all these areas so while the cost of coatings are less than 0.5 percent of the total selling price, it can represent the success or failure of the package,” he continues.
Coatings provide an extra layer of durability to protect the packaging from damage during the converting, filling, and shipping process. “Nothing looks worse on a shelf than a scratched and beat up package,” admits O’Boyle. Scratch-resistant coatings ensure print jobs maintain attractive aesthetics until the consumer sees it on the shelf.
According to O’Boyle, some coatings change the packaging surface’s slip to allow for freer movement through and around the processing equipment, which increases line speeds. For example, Sun Chemical’s heat- and cold-seal coatings help in a sealing and closing of the package. They even increase the coefficient of friction of the package’s surface, allowing packages to be better and more stable during stacking.
Additionally, using a coating can protect the print and substrates from environmental elements like grease, humidity, oil, UV light, and water. Coatings that protect the contents of the package from the environment and the package from its own contents are known as barrier coatings.
O’Boyle says barrier coatings provide benefits like increased shelf life or product usability that would otherwise be gained by additional substrate layers or heavier substrate gauges. “By using a coating in place of more substrate, coatings provide significant light weighting and down gauging of the package with less total material mass to do the same job,” he explains.
Coatings provide a variety of properties for digitally printed packaging applications and cover a range packaging types like flexible packaging, labels, and folding packaging. Coating types are selected based off application, equipment, ink, substrate, and end use.
According to Vogel, coatings are manufactured based on the intended substrates and equipment. Several factors determine which coatings are needed for specific equipment like dry speed, durability, food contact, gloss range, inline or offline, material cost, recyclability, required energy, rub, spot applications, visual effect, and volatile organic compounds.
Coatings should also match the ink used and be tested before applying to the finished packaging. For analog printing, Vogel says many coatings are used universally but as packaging becomes more complicated, marrying the coating to the ink becomes increasingly critical.
For flexible packaging, coatings are used to adhere materials together and sealing through contamination. “Functional coatings provide oxygen and moisture barriers that improve the packaging,” says Arica Drake, marketing manager, flexible packaging, Michelman, Inc. She believes overprint varnishes provide the ability to enhance shelf appeal while providing an added effect like texture.
Many digitally printed labels need a coating for ink to adhere to the media. Drake says labels also need overprint varnishes to protect the inks in both manufacturing and distribution.
Functional coatings that provide oxygen, grease, and mineral oil barriers are essential for folding packaging. Kevin Gillie, group technology leader, printing and packaging, Michelman, says mineral oil protection is a real concern in Europe and as a result, barrier coatings are used to prevent migration. “Consumer good companies and brand owners don’t want to be in the headlines because mineral oil has migrated into their products like crackers or cereal,” explains Gillie.
According to O’Boyle, inks that will be coated should be free of surface modifying additives, like silicone, which can affect the smoothness of the coating going over the top and make the slip harder to control. “With certain coating chemistries, pigment selection in the ink is important and you need to stay away from alkali sensitive pigments,” he adds. Alkali sensitive pigments can cause color shifts or ink burnout during coating. Additionally, fluorescent pigments and pastel inks may color shift when used with aqueous or UV coatings.
Food and beverage packaging have specific coating requirements for direct contact with edibles. While protecting the package and increasing shelf life, these coatings also help brand owners manage supply chains and enhance the package’s aesthetics.
Vogel says it’s a general understanding that UV coatings are not used for food packaging unless there is a proper barrier between the UV coating and food product. Some aqueous coatings are FDA compliant and are often used in conjunction with food packaging due to organic and water-based makeup. Packaging manufacturers can contact coating companies to determine if coatings are compatible for direct or indirect food contact.
Barrier coatings can be used for paper- and paperboard-based food service items like paper cups, plates, and trays. O’Boyle says this is because barrier coatings are specially designed to be compliant with FDA regulations for direct food contact and can provide the grease, water, and heat resistance that might otherwise be gained by using polymeric layers. “By using coatings instead of polymers, paper and paperboard can still be easily repulped and recycled, greatly improving the ‘green’ footprint of the item,” he continues.
To help manage a large number of SKUs with similar graphics, packaging manufacturers use laser coatings, which allow them to add information to both secondary and primary packaging after filling and closure, especially for food packaging. According to O’Boyle, these coatings are used for practical supply chain purposes or as a late-stage brand differentiator. The solution is also compatible with a variety of substrates and printing processes including flexographic printing.
“It involves printing a patch of a specially developed transparent or tinted coating onto the generic packaging stock at the artwork printing stage,” says O’Boyle. The coating reacts to a low-power carbon dioxide or fiber laser to produce a black image, which enables the converter to add high-contrast coding information after filling and closure without complicating the packaging process or risks to the product.
Some coating manufacturers have groups dedicated to food safety that coordinate with government agencies like the FDA and EPA or use internal experts, universities, and outside labs for verifications. “It’s worth mentioning that formulation ingredients are cleared by the FDA for use in food packaging but not approved,” shares O’Boyle.
There are also no third-party approvals for coatings used on food packaging. In the U.S., Vogel says companies can only stipulate what the coating is compliant to and then list the regulation to which they are compliant.
Other countries have similar organizations with their own regulations that vary. “This makes it very important that coating manufacturers have experts that can interpret the regulations,” says Gillie. Experts survey the different materials in the formulation and examine how they compare to regulations. Additional testing is performed to examine how coatings react, perform in different environments, and for potential harmful effects to consumers.
Inline or Offline
For analog printing, coatings are generally applied inline. But for digital printing, Vogel says coatings are most likely applied offline with some exceptions. He believes inline can be more effective for standard production, especially if the printer is also finishing a product inline, like die cutting.
However, offline coating equipment may have a faster speed than a digital printer. “A single coater could handle the output of two or three printers,” says Vogel. During spot coating, he says offline coating may be more effective due to the time required for setting up the equipment.
O’Boyle believes inline applications are preferred for ease of workflow if the coatings can match the speed of the printing equipment. “Other coatings that can run at faster speeds are more economically run on high-speed offline coaters while special effect or high-coverage coatings can be run at slower speeds on an offline coater without impacting the printing operation.”
Despite speed, Gillie believes that inline is sometimes viewed as more efficient because there are less steps and less chances to damage the material by eliminating additional unwinding and refining of the material, which can cause wrinkles and creases. However, he warns that some organizations might not have a coating station at the end of their film line and will have no other option but offline equipment. “Organizations need to understand their run sizes and determine what process will provide the best quality and most cost-effective way to produce.”
Applying Offline Coatings
According to Vogel, four types of coating equipment are offered for offline coating. This includes roller, gravure, rod, and anilox coating.
Roller coating devices are commonly used in manufacturing. They are available in a variety of types including paint rollers and coating machines. The roller device transfers the coating from the roller’s surface to the packaging surface. “Roller coating still dominates the market because it is a lower cost and generally UV only,” says Vogel.
Gravure equipment is a contact process that roll coats with forward and reverse operation. It is generally equipped with an enclosed feed chamber. According to Vogel, gravure equipment is often used to coat high-volume packaging.
Rod equipment includes a wire wound rod that is applied across the packaging and smooths the coating over the surface. The wire’s diameter regulates the coating’s thickness and the groove allows the proper amount of coating to pass through. Because it provides consistent film weight, Vogel says it’s often used for specialty roll-to-roll applications.
Anilox coating uses a hard cylinder that is coated by a plate that contains fine dimples. For coating packaging applications, Vogel says this type of equipment is gaining ground. “While more expensive, it can run aqueous and UV coatings, apply UV special effect coatings not available for roller and rod equipment, and spot coat,” he shares.
Coating Packaging Applications
Coatings for packaging applications improves durability during processing and repeated handling by customers. Coating types vary based on labels, folding packaging, and flexible packaging, however, manufacturers should always select a coating type based on intended substrates and inks to ensure compatibility. As digital print technology advances, special coating effects emerge like metallic or textures.
Mar2018, Industrial Print Magazine