By Melissa Donovan
Digital printing technologies are capable of printing to materials used in flexible packaging applications, however it is only one step in the process. Lamination of two films by means of an adhesive is the most common technology used to assemble the base structure in flexible packaging for reverse print applications. This type of lamination bonds two layers of film, foil, or paper using adhesive.
Three common adhesives are used to bond layers of flexible packaging together—solvent based, solventless or solvent free, and water based. All three are used to construct flexible packaging. To fully bind all of the layers together, the piece is put through a curing process referred to as polymerization, which is completed on a dedicated machine designed to apply the adhesive.
Above: Ashland’s laminating adhesives present new possibilities for flexible packaging in place of traditional packaging.
A Trio of Adhesives
To understand the various types of adhesives, Justine Hanlon, market manager flexible packaging, H.B. Fuller Company, provides a rundown of each.
Solvent-based adhesives are typically easy to use and offer a range of bonding and application settings. They also provide a clean print on metalized surfaces and specialty print jobs due to superior performance, shares Hanlon. However, they contain volatile organic compounds (VOCs).
H.B. Fuller’s flexible packaging solutions and materials address the rapid growth and rigorous requirements of the flexible packaging industry. The company’s line of flexible packaging solutions and materials includes Flextra solvent-free and solvent-based adhesives for film, paper, and foil laminating.
Solventless adhesives are formulated without solvent and have low VOCs. While they feature good running speed, cure times are longer.
Water-based adhesives are what Hanlon refers to as heterogeneous systems. They are comprised of a solid polymer phase dispersed in an aqueous phase. Benefits include no VOCs, fast run speeds, cost competitive, and easy to clean. However, they don’t have a strong chemical or heat resistance and require a large amount of energy to drive water off the substrate.
For those adhesives most commonly used in digitally printed flexible packaging, Catherine Heckman, global industry manager, Ashland, says solvent free and solvent based are the most widely used, with water based not as common due to performance limitations in thermal resistance and poor moisture resistance.
“Water based would be used more in an overlaminate where the digital print needs to be protected. A catalyst is recommended to be used with the water-based adhesive to provide improved performance properties,” she suggests.
Heckman notes that in the aforementioned example she is referring to HP, Inc.’s inks used with laminating adhesives when discussing digital printing technology.
Ashland provides innovative technology solutions for a range of narrow-, mid-, and wide-web applications. Its laminating adhesives open new possibilities for using flexible packaging in place of traditional packaging. Faster curing adhesives improve converters’ productivity. The company’s extensive product line of pressure-sensitive adhesives, functional coatings, and primers are formulated to meet customers’ most stringent requirements in areas such as food and beverage, shipping, transportation, health and beauty, industrial, postage, and security printing.
The efficiency and cost savings digital print presents in regards to shorter runs is advantageous for many. Brand owners can inexpensively order limited edition or customized packaging by country, state, or household. Those in the food and beverage industry understand these benefits, however they require adhesives that provide little to no potentially harmful chemicals.
In Packaging Adhesives Market Size & Share, 2018 to 2025, an industry report by Grandview Research, it was cited that globally, about 50 percent of the total packaging products manufactured are utilized for food packaging. Flexible packaging applications used for food, in terms of revenue, accounted for a market share of around 33 percent in 2016.
“Food safety is one of the primary concerns and top priorities for developing new packaging adhesive products,” states the Grandview Research report. To address these concerns and to effectively satisfy the demand coming from one of the largest segments using flexible packaging, adhesive manufacturers work to advance products.
According to Heckman, Ashland sees increased interest and capital investments made in solvent-free adhesive laminates that provide food compliant low-migration properties. She also points to UV LED laminating adhesives as an emerging technology that could overshadow water-based adhesives as the next environmentally, food safe offering.
“New technology enables faster run speeds of up to 1,000 feet per minute and increasing processing and cure times, which enable converters to bring products to market. As long as the ink is compatible, the newest formulations use the relationship between the adhesive, primer, and ink to create seamless, quality lamination,” explains Hanlon.
Into the Water
Water-based adhesives are improving, however advancements still need to be made for the product to equal the durability and other robust characteristics of its solvent based and solventless counterparts.
Hanlon says that despite water-based adhesive being around for awhile, it still struggles to overcome the bias that it can’t compete with other technologies in regards to chemical and heat resistance. “There is a lingering perception that if you’re going to create an expensive structure, water based isn’t the adhesive technology to use. Gains have occurred within energy efficiency, but there is still an energy cost associated with driving water off the substrates,” she continues.
“Water-based adhesives still need improvements in moisture properties and thermal resistance to be able to match up against solvent-free and solvent-based technologies,” admits Heckman.
According to Packaging Adhesives Market Size & Share, 2018 to 2025, in North America developments in technologies and innovative techniques for manufacturing environmentally friendly adhesives are expected to be major factors driving the water-based adhesives market.
Guidelines to Follow
Converters, printers, and manufacturers need to be aware of multiple regulations before choosing and deciding on an adhesive for flexible packaging. This is whether or not the packaging involves contact with edible substrates, as other concerns involving the environment and fire safety should also be considered.
For food and beverage, two important regulations in North America are from FDA 175.105 and 177.1395. Outside of the Americas, Nestle and Swiss Ordinance are good references to maintain compliance. Environmental concerns involve rulings from PAA decay, OSHA ventilation, EPA waste disposal, and TSCA.
“The adhesive chemistry and product end use have a direct impact on which regulations and guidelines are going to be applicable. Although the regulations can be confusing, our company has a global regulatory group that can make sense of all international regulations and can aid customers in understanding their part in the regulatory process,” shares Hanlon.
Similarly, Ashland offers a PhD toxicologist working closely with customers to provide education on regulations, migration standards, and manufacturing practices to choose the best adhesive for the application.
Adhesives compatible with digital printing technologies and used in manufacturing environments creating flexible packaging continue to evolve. Part of the changes are necessitated by the use of digital printing in food-related packaging. As more brand owners understand the benefits of digital print—namely short runs, which enable more customization and limited time offer options—the demand for adhesive compositions that work well with digital print continue to grow.
Sep2018, Industrial Print Magazine