by Industrial Print Magazine
Labels require a certain degree of durability no matter what they are adhered to or for how long. Sometimes, the application necessitates an additional degree of protection. Durable varnishes or coatings are used for enhancing the label resistance of digitally printed pressure-sensitive labels for products such as personal care, household, chemical, beverage, and pharmaceutical applications.
Above: Deco Chem offers functional inks and coatings.
Labels must hold up to the vigorous process of manufacturing, shipping and handling, and especially human handling in all types of environments. Products that utilize labels benefit from the enhanced durability offered by varnishes and coatings.
In any scenario, protection should be considered throughout the entire production process. “Protection requirements must be taken into account for each product as it goes through the packaging line, to the shipping requirements, to final end use,” explains Clint Price, technical product manager UV labels, ACTEGA North America.
Labels cannot fail before the product’s end of life. As Nick Scheinkonig, technical marketing manager, EMEAI, Lubrizol Performance Coatings, points out, durability of the final printed label is critical. “Key information printed on labels including composition, product safety, usage instructions, and regulatory requirements must be legible for all to see. This does not only apply to the end user. For instance, in a scenario where goods are damaged in transit, anybody handling the goods must be able to read the labels. Highly durable coatings provide an increased level of robustness to the label to deliver the needed protection.”
“Adding a coating to protect the label significantly increases its lifespan and ensures that it survives until the product packaging is discarded by the end consumer. For example, applying a top coat to a flow wrap for a product like a chocolate bar wrapper applies the benefit of wear resistance and strength to the material with the additional barrier of protection,” notes James Gazdick, marketing manager, Deco Chem, Inc.
Specific products might require further protection. Personal care, household, chemical, beverage, and pharmaceutical labels benefit from a varnish or coating to enhance their durability.
For example, a shampoo bottle label must be resistant not only to all it will encounter during the production and shipping process, but also “to the continued cycle of use in a damp environment to ensure there is no label degradation during the life of the product,” says Price.
Gazdick adds that household products benefit the most from the addition of a varnish or coating as they have a longer utilization period with the end consumer. For example, Deco Chem produced coating for a popular syrup company’s label. “An additional layer of protection was required in this case as this is a product that will go through many dramatic changes in environment and temperature, as well as spend a long period of time with the consumer after it leaves the store shelves.”
Many of the consumer products in these categories have certain contents that could damage the label, which is also something the buyer needs to think about when determining additional protection. “The contents inside the bottle or container could also be an issue. For example, if the contents are what we consider hard to holds, like sunscreen, shampoos, witch hazel, or hand sanitizer. Suppose those contents regularly spill out of the container with normal use. In that case, the packaging buyer needs to be aware that that could eat away at the label, and more durability considerations should be taken,” says Tom Hauenstein, VP of sales, S-One Labels & Packaging.
Varnishes or coatings add a new level of opportunity to those digitally printing the labels for personal care, household, chemical, beverage, and pharma applications.
“The majority of digital printing done today does not have these requirements without the use of a protective layer, and therefore the needs of the brand owner are as such that these coatings become more necessary than ever before for scuff, water, solvent, and acid resistance,” shares Price.
In addition to enhancing protection, varnishes and coatings serve other purposes like visual and haptic effects.
According to Scheinkonig, labels are a part of overall product branding, such as in personal care products sold directly to consumers. “In these applications, coatings can deliver some impactful visual capabilities, such as enhancing the brightness and sharpness of colors, or to manage gloss or texture effects, to name a few.”
“The combinations of gloss, satin, and matte surface appearances can create a sense of motion that is appealing to the eye of the consumer, and therefore make packaging stand out from the crowd on the shelf. Soft touch and tactile varnishes are great ways to enhance the feel of the product and give the consumer another level of satisfaction,” shares Price.
Different types of materials or substrates are used for labels found on personal care, household, chemical, beverage, and pharmacetical applications. Not all of them call for a coating or varnish, but they could benefit from them depending on the buyer requirements.
Paper-based labels are commonly used. Price says these often require overprint varnish with higher resistance properties. “These will readily absorb most materials that the label comes into contact with and possibly degrade the inks much quicker than if the label had a robust protective coating.”
Biaxially oriented polypropylene (BOPP) is another material for labels used in these applications, but Price says they normally don’t require overprint varnish, however depending on the end use it may still be a requirement.
“Typically, a non-porous substrate will be more robust in a harsh environment than a paper product. We see a lot of BOPP in the durable label environment for that reason. If you had a paper label on a shampoo bottle, the varnish hardly matters if the paper underneath the ink and the varnish begin to fall apart,” notes Hauenstein.
Films and plastics benefit from a coating prior to being printed, as they present challenges regarding adhesion. “Printing directly to these substrates without the right coating is difficult as the ink has nothing to which it can anchor,” says Scheinkonig.
Don’t Forget Ink
Certain types of ink—inkjet or toner—find advantages with varnish and coatings.
“All types of inks benefit in some way from a coating or varnish, such as to achieve better adhesion, dry time, and image quality. The ultimate driver may depend on the absolute requirements of the end application,” shares Scheinkonig.
Hauenstein agrees, stating that it is “rare—regardless of ink type—that material goes out the door without some sort of coating over the top of it, whether it be to grab consumer attention, provide mechanical resistance, or water/chemical resistance. However, digital inks are known to be more fragile than conventional printing methods and, therefore, may require a more robust varnish or a heavier coatweight to combat that fragility.”
Aqueous-based inks almost always require a coating, according to Scheinkonig. “This is because they are not instant dry/cure, as is the case for UV inks, for example. Instead, a drying stage is required to remove the water, and a coating can help facilitate the process by providing increased absorbency to the substrate. This is of particular importance when printing on films—and other less or non-absorbent substrates. In contrast, very absorbent materials, such as uncoated paper, pose a different challenge. Aqueous-based inks tend to dive in and spread very rapidly, resulting in loss of color strength and image sharpness/bleed. Fixatives in coatings can trap inkjet colorants in place, preventing unwanted migration.”
“UV LED inkjet inks have increased chemical resistance over water-based inkjet due to the cross linking that occurs during the curing process of UV LED inkjet. Water-based inkjet has the lowest chemical resistance with dry toner being somewhere in the middle. These would both benefit greatly from overprint varnishes,” summarizes Price.
Some other trends to be aware of involving durable varnishes or coatings used for enhancing the label resistance of digitally printed pressure-sensitive labels for products such as personal care, household, chemical, beverage, and pharma applications involve the composition of the coatings themselves, how they are cured, and appearance.
In terms of composition, Price says “high-performing epoxy acrylates and urethane acrylates are becoming increasingly popular to improve the backbone chemical resistance for many of these applications. Carefully selected silicones that are incorporated into the acrylate chemistry and become an integral part of the chemical structure are becoming a staple to the needs of the overprint varnishes for these brand owners.”
An increasing number of companies are reformulating their coatings to be designed for digital inks, according to Hauenstein. “Other manufacturers are offering a suite of additives for UV coatings that enhance the durability of the coating, and those additives can be added press side by the operator to give the labels that extra layer of durability.”
Gazdick brings up curing, noticing more label manufacturers switching to UV LED from mercury vapor bulbs. “The formulation of our clear coating inks is done in such a way as to utilize the wavelength frequencies of the LED curing system enhancing the overall result of the cure. In addition to a stronger cure, LED equipment also boasts of cheaper equipment costs, maintenance, operation costs, and it provides a cleaner way of curing ink that results in a lot less waste.”
Regarding appearance, Scheinkonig sees an increased interest in glossy, transparent coatings for applications like personal care products and customized beverage cans. “A typical goal is to achieve high levels of gloss and maximum image quality, while being optically transparent on the substrate. In terms of ink types, aqueous-based inks again pose the biggest challenge with regards to ink dry time. Developing ink-receptive coating technologies that are very absorbent but also optically clear are fundamental to the success of these types of products.”
Coat It, Varnish It
Coatings and varnishes are popular add ons to digitally printed labels, especially those used in personal care, household, chemical, beverage, and pharmacetical applications. These products are in need of an extra layer of durability, no matter the material the label is made out of or the type of ink used to the print the graphic.
Sep2022, Industrial Print Magazine