Understanding Adhesives

Labels and packaging lead more complex lives than meets the eye. Some labels and packages need to withstand the frigid temperatures of a freezer, and others must survive outdoor elements for several years. Others may even need to adhere to multiple surfaces. Adhesives are often the unsung heroes in this equation and yet, they ensure a label sticks to its intended surface, help a package maintain its physical integrity under extreme conditions, and play an integral role in protecting both the product and consumer.

Understand Your Application

Selecting the proper adhesive for a label or packaging product should begin by developing a complete understanding of the final application. Mike Witte, director of national accounts for pressure sensitive for Franklin Adhesives and Polymers, explains that before an adhesive is selected, there are three essential details to iron out.

Temperature and humidity are important considerations when selecting a label adhesive for food applications. Photo courtesy of Franklin Adhesives & Polymers.

The first two are apparent: establish the material the label is made from and the surface material it will stick to. Since different adhesives bond to some surfaces better than others, it’s essential to find a solution that adheres to both the label material and its target surface.

Witte says the third aspect to identify however, is a bit more complex. Understanding the temperature and humidity of the various environments the label will be subjected to is imperative in choosing the proper adhesive.

“For example, for a label that would go on frozen poultry like turkey, you might want something that’s going to be capable of establishing adhesion even though there might be a very thin layer of condensation on the exterior of the surface that label is going to stick to,” Witte says.

Market segment also plays an important role in deciding on the proper adhesive to use in a packaging project. Michael Trakhtenberg, technical director for ICP Industrial, which manufactures the Nicoat and MinusNine coatings and adhesives products, explains that the requirements for an adhesive to be used on a food or medical package are drastically different than the requirements placed on a product package outside of those market segments.

Much like migration requirements that are placed on inks, Trakhtenberg says that adhesives can also undesirably pass through a barrier on a package. “If there is a known barrier or tested barrier that nothing migrates through, that’s one side of the story,” he says. “But if the barrier is not really a barrier, or a poor barrier, that’s a totally different requirement for the adhesive.”

Levels of Stickiness

Particularly in the labels segment, Witte explains, choosing the right adhesive can also depend on how long a label is meant to stick to its intended surface. He says that a label can fall into one of three categories, depending on the desired permanence of the label.

A typical example of a permanent label, Witte explains, is a warning label on outdoor power equipment, such as lawnmowers, chainsaws or other gasoline-powered products. An adhesive for one of these end-uses may also require additional strength to stay in place after coming into contact with gasoline, outdoor elements and high temperatures. Witte says permanent labels are also prevalent on ladders, providing safety information while withstanding outdoor conditions and potential abrasions over several years.

Permanent adhesives are often used on warning labels, such as those found on ladders.

“These are permanent labels and are not intended to ever be removed because they have information that’s important every time the device is used,” Witte says.

Shipping and address labels are also common applications for permanent adhesives, as are price-marking labels and postage stamps. Permanent labels are often used in tamper-proof packaging, and in price marking, in which a label cannot be removed without destruction of the label. Other security-related labels make use of permanent adhesives.

On the opposite end of the spectrum, Witte says removable adhesives are often used on labels that appear on an in-home appliance or a smartphone. These labels may provide important user information, but are not meant to remain on that product forever. While making a label easy to peel off of its surface is one part of a removable adhesive’s job, Witte explains it’s also imperative that it does not leave any unsightly residue behind.

Finally, a repositionable adhesive allows a label to stick to one surface, be removed, and then stick to a completely different surface. Witte says a popular usage for this type of material is for advertisement labels that often appear on the front page of a newspaper. For example, Witte says a pizzeria could have a label with its contact information placed on a newspaper. Then, when a customer receives the paper, he or she can remove that label from the paper and place it on the refrigerator, keeping the company’s phone number in an easily accessible location.

Advancements in EB

As electron beam (EB) curing has advanced in the drying and curing of inks, its benefits are also being realized in adhesives. Trakhtenberg explains that in terms of migration, EB curable adhesives are ideal because they lack photoinitiators, which are materials known to have migration qualities.

In the label and flexible packaging segments, which often feature reverse printed applications, Trakhtenberg explains that EB curable adhesives can provide additional benefits. Because UV light has limitations penetrating a surface that is not transparent, EB becomes an optimal solution for reverse printing.

“If you have a substrate that is reverse printed, the UV light is not going to be able to do that,” he says. “So from that perspective, an EB adhesive would be the most advantageous.”

Trakhtenberg also relays that Nicoat has been involved in an exciting development for EB laminating adhesives in the flexible packaging segment. During drupa, through a partnership with press manufacturer Uteco and ebeam Technologies, Nicoat was part of the unveiling of a system that instantaneously laminates two separate films together with a bond strong enough for flexible packaging applications.

“In cooperation with [Uteco and ebeam] we did a lot of work upgrading the laminating adhesive that would be capable of laminating a variety of different films on that machine — everything in-line with the EB curable inks,” Trakhtenberg says.

Clear Communication

Because the type of adhesive in use can vary drastically between applications, communication with suppliers is necessary to ensure the proper choice is made and a label or package doesn’t end up too sticky, or not sticky enough.

As Witte says, there are important differences in the adhesives used on a label that only needs to stick to a surface for an hour and an adhesive that can keep a label in place for more than a decade.

“The main thing to look to is to have a very clear understanding of label stock, the target surface, the environmental conditions and how long a given label is going to have to do its job,” he says.

Trakhtenberg explains that particularly in food and medical packaging, the earlier that communication process starts, the better. If there are migration concerns with the final product, the converter and supplier can work through those together, preemptively stopping any potential issues in their tracks.

“The most sophisticated people know that they need to communicate with us in the very early stages,” he says. “If we’re talking about food packaging, it is critical that we technically collaborate with customers at the earliest stage possible.”