Adhesives are complex and require far more than simply slapping some glue on a label and applying.
Nowadays, pressure sensitive adhesives must adhere to an object under a wide range of conditions, including hot and cold temperatures, wet conditions, and situations with durability concerns. In addition, the adhesive must withstand normal rigors of everyday life that occur during shipping and handling.
Not all adhesives and substrates are created equally, either. Depending on the application, some adhesives work better with certain substrates as opposed to others. “Successful label adhesives meet a variety of requirements, but all adhesives must meet manufacturing and performance requirements,” explains Kirit Naik, R&D director, Americas, UPM Raflatac. “For manufacturing, the adhesive must be stable during its mixing, coating and drying processes, then diecut and converted well for the customer. It must also interact properly with the other components in the laminate construction, such as anchorage to the face material, stable release from the silicone, and so on. At the end user level, the adhesive must meet all performance requirements such as adhesion to specific substrates. This means surface energy, roughness, moistness and removability.”
Pressure sensitive adhesives are typically classified as permanent, removable or repositionable. Permanent adhesives create a strong bond, and the label or object will often be damaged if the label is removed. Removable labels can be adjusted for a frame of time following application. These adhesives are frequently more sensitive to conditions like humidity and moisture, though. Finally, repositionable adhesives can eventually become permanent, but they allow for some adjustment following initial application.
R&D teams at leading labelstock and self-adhesive material suppliers continue to push the envelope, as technology has improved significantly in recent years. According to James Akeley, global adhesives technology leader at Avery Dennison, the industry is seeing a general trend away from solvent-based adhesives – solution acrylics and solution rubbers – because solvent-based adhesives carry associated hazards.
Wherever possible, adhesive development companies strive to replace solvent-based adhesives with safer, less regulatory constraint adhesive technology such as hot melt and emulsion. “There’s been an emerging trend lately for 100% solvent-free acrylics, and those are warm melt acrylics that are UV-cured and are no longer flammable because they’re solvent free and they’re cured on web via UV light,” says Akeley. “Those are emerging, and the only reason they haven’t taken the world by storm is because they’re expensive from a technology platform standpoint, and a number of heritage coating assets around the world aren’t yet equipped to process UV technology.”
Akeley notes, though, that solvent-based adhesives still have a place in the industry. “They still play a role in durable labels, highly chemical-resistant labels, labels for marine environments and very high heat resistant labels because they drive a certain performance attribute that emulsions and hot-melt can’t quite get to,” explains Akeley.
There are other trends in adhesive development, explains Kim Hensley, marketing manager at Mactac. “Today’s adhesives provide excellent clarity, non-water whitening and a high-service range,” Hensley says. “Adhesives are designed to withstand harsh environments and temperatures ranging up to 400F and beyond. Prior to this advancement in adhesive technology, most PSAs couldn’t withstand temperatures of more than 300-325F.”
While the technology has improved, the adhesives segment still deals with a range of challenges – specifically cost versus performance. “There’s a ceiling where a label’s performance needs to deliver under a certain cost to maintain viability as a decorating technology,” says Akeley. “Performance typically is finite if cost is finite.”
Other challenges include environmental conditions, such as high heat or high moisture. These challenges occur in specific applications, and companies must navigate the pros and cons of different solutions. “Often times when you’re trying to hold onto specific performance attributes, you might have to sacrifice other attributes to achieve that and then tradeoffs need to be balanced,” explains Akeley.
According to Avery Dennison’s Akeley, label adhesives are normally classified along a continuum of either application or performance. “From a performance standpoint, an example would be a high-performing adhesive, perhaps a durable adhesive, where the label is intended to stay in place for multiple years, and then we move to a general purpose adhesive,” says Akeley. “We then move further back along the removable continuum, where we have repositionable, removable and ultimately ultra-removable adhesives, where removable labels are intended to peel and reseal repeatedly.”
The application classification typically spans a temperature range or other environmental criteria such as moisture. “An all-temp adhesive would be an example of an adhesive that’s designed to adhere under room temperature and cold temperatures,” explains Akeley. “There are also freezer grades, other speciality type grades like direct food contact adhesives, as well as pharmaceutical or medical grades.”
Freezer grade adhesives involve low temperatures. There are also cryogenic adhesives that need to adhere to materials in unique situations like a liquid nitrogen environment. Cryogenic adhesives might be used for specialty medicines.
“Cryo-adhesives is a trend that’s been steadily growing over the last 10 years, but that’s an extreme case as there’s only a small subset of adhesive chemistries that might even perform,” says Akeley. “In a standard range, freezer grade is typically the lowest, and there you’re talking about -20 degrees Fahrenheit as a low. And then as an upper end, we don’t typically talk about labels that adhere above 150 degrees Fahrenheit.”
Adhesive properties might include peel adhesion, cohesive strength, as well as dynamic mechanical analysis. At that point, tests can then be used to characterize different label adhesives. Mactac’s newest product is designed to meet the needs of cold temperature adhesives. “Mactac offers permanent, removable, acrylic and hot melt adhesive solutions to meet all of our customers’ needs,” says Hensley. “Our newest adhesive launch is CHILL AT. It’s no secret cold temperature label applications can be challenging. Cold temperatures can cause labels to lift or peel. If condensation occurs, there’s a chance the label could fall off completely. And, in extremely cold cases, labels have been known to stiffen and lose their strength. Our customers have long needed a label solution that would stick quickly and stay in place as needed when temperatures go below 40 degrees Fahrenheit. However, they also often stress how great it would be to have one go-to label solution for any application need. So, our thought was: ‘Let’s develop an all temperature label specially formulated for demanding cold temperature applications, but that also works great at room temperature too’.”
Passing The Test
Adhesives require meticulous compliance testing and safety measures, especially as they relate to food products. There are different governing bodies throughout the world that set the standard for acceptable adhesive practices. In North America, the Toxic Substances Control Act (TSCA) regulates adhesive chemistries and how companies construct polymers. In Europe, REACH governs these practices, which can put constraints on companies when they’re attempting to manage global product lines. These regulatory bodies must also qualify key raw materials that go into adhesives.
According to Henkel, the “REACH Regulation marks a fundamental reform of European chemicals legislation. REACH regulates the registration, evaluation, authorization and restriction of chemicals.” The goals of these legislative bodies are to improve the safe handling of chemicals and protect human safety, as well as the environment.
When dealing with food applications, Mactac’s Hensley says the following are some of the most common regulations: Direct Food Contact – 21C.F.R 175.125, where labels are applied to poultry, dry foods, and processed, frozen, dried, or partially dehydrated fruits and vegetables. Then, 21C.F.R175.125 deals with labels applied to raw fruits and vegetables.
According to Avery Dennison’s Akeley, product compliance teams – particularly for those companies with a global reach – must navigate how their adhesive properties are governed throughout the world. “Most recently, China has rolled out their own regulatory system that’s kind of a combination of TSCA and REACH but unique in its own way,” he says. “So it requires a pretty savvy product compliance team to make sure multinational companies stay ahead of the game while also offering the right solutions to customers.”
Adhesive manufacturers maintain their own set of quality control measures too. Avery Dennison uses a number of methods to satisfy multiple manufacturing processes across a value stream. “Since Avery Dennison makes their own adhesives, we have specific quality and qualification processes at the adhesive manufacturing scale and then at the coating level, where we coat these adhesives and then make labelstock out of them,” says Akeley, who works at Avery Dennison’s Center of Excellence for Adhesive Development and Manufacturing for North America. “We have statistical tolerancing processes to verify we have the proper parameters to make the adhesive, to test whether we’re seeing the proper adhesive properties as we’re changing variables.”
Avery Dennison’s project team will then periodically reconvene to analyze new data that has been gathered during production manufacturing. This ensures that the adhesive is meeting the demands that it was intended to.
When starting an adhesive development project, UPM Raflatac works with business groups to identify Critical To Quality (CTQ) parameters for performance and works with its vendors to identify raw materials to use in its formulations. “During the formulation phase, we optimize the mixture of components for performance and processing,” says Naik. “We use analytical methods, such as dynamic mechanical analysis, performance testing, such as tack, peel and shear, and simulate any end use properties like removability from specific substrates, BS5609 screening, to ensure our adhesives will meet our customers’ requirements.”
According to Hensley, a new label adhesive needs to be tested and compared to existing adhesives, as well as competitive adhesives, for room temperature tacks, cold temperature tacks, and various substrates, including stainless steel, HDPE, corrugated, glass and polypropylene. The product may also need to be sent in for FDA, UL or BS5609 compliance. There are various ways to test or measure how surface conditions can affect adhesive performance.
“Initial tack is used to define how quickly a bond is formed between adhesive and surface. If initial tack is high, adhesion to the surface will be high,” explains Hensley. “Peel strength determines the strength of adhesive bond to the surface by measuring the force needed to break the bond using standard parameters like peel angle or direction, application pressure and time of bond. Shear resistance shows the durability of adhesive bond. A high-shear adhesive is firmer and doesn’t flow into a surface as well, equating to lower initial tack, but making it less likely to split if stressed.”
Adhesive technology has improved in recent years, enabling labels and packaging to be more efficient. Some of the most innovative enhancements have targeted the foods segment, specifically with reclosure applications.
“There are some really great packaging innovations taking place as it pertains to food,” says Akeley. “You’ve seen the emergence of reclosure labels for dry goods, well reclosure is emerging in other areas like the refrigerator section and in meats and cheeses. There’s a lot of really unique innovation going on in food packaging design that is triggering efforts further upstream in the adhesive design.” While sustainable initiatives are present throughout the labels market, these “green” processes are perhaps no more present than in the adhesives space. Avery Dennison has taken a number of measures to promote environmental safety. “Even in times where oil prices are low, sustainability efforts are still taking place, and Avery Dennison has some very laudable goals around sustainability where we’re trying to be landfill free and we’re optimizing our own manufacturing processes to use less energy,” explains Akeley. “The chemicals that we buy are intended to conform to environmental and socially guiding principles. As we develop new adhesives and new labelstocks, these philosophies become a part of that design space for us.”
In this space, Avery Dennison has launched its CleanFlake portfolio. CleanFlake adhesive technology is designed to address PET plastic recycling. The portfolio features a water-based, recyclable adhesive that allows the facestock and adhesive to cleanly separate from the PET flake. Since no adhesive residue remains on PET flakes, there is no risk of contamination.
“It’s an adhesive label combination proprietary to Avery Dennison that allows bottle recyclers, particularly high-volume recyclers, to grind the bottle up before they have to remove the label,” says Akeley. “In subsequent washing baths, the adhesive and label combinations are designed to detach from the flakes of bottle plastic and essentially float so that the recyclers can easily remove that labelstock material from the recycled plastic flakes.”
According to Avery Dennison, CleanFlake is available in clear or white BOPP film facestocks and a 54# semi-gloss paper. The technology passes the highest form of testing available from the APR.
Not only are companies rolling out new adhesives, they are becoming more proactive with quality control measures. In order to stay ahead of the curve, R&D teams are more heavily scrutinizing compliance complexity and screening. According to Akeley, companies are incorporating more rigorous testing in order to help “design the products of tomorrow.”
The adhesives market has been ripe with mergers and acquisitions, as well. H.B. Fuller, for example, has acquired Wisdom Worldwide Adhesives, Cyberbond, and Advanced Adhesives in the past calendar year. These moves are designed to leverage broader technology portfolios throughout the world.
In order to enhance its hot-melt adhesives, Henkel acquired Novamelt in 2015. The privately-owned German company enabled Henkel to leverage solutions predominantly used for self-adhesive labels and tapes. The UV-curable hot-melt technology is designed to withstand high temperatures and heavily changing weather conditions.
Digital printing is a priority in the adhesives market, too. Ashland recently collaborated with HP, Inc. to develop laminating adhesives and coatings that are compatible with HP Indigo ElectroInk. The partnership is meant to further the proliferation of digitally printed labels and packaging, but that’s another story altogether.
Ryback and Ryback has partnered with Fujifilm to develop a new Universal Seaming Adhesive (USA) for the shrink sleeve industry. This new product will change the way shrink sleeve manufacturers get products seamed. R&R will be the exclusive distributor of the product throughout the world.
Universal Seaming Adhesives are formulated to be used as a true adhesive for the seaming of shrink sleeves. They can be used on PVC and PETG shrinkable substrates. Unlike existing seaming solvents that melt the film, and the actual substrate to itself, USA forms a true mechanical bond, which allows both edges of the finished tube to be glued to each other.
There are several advantages of using an adhesive over conventional solvents in the market today:
- The biggest advantage is that the adhesive forms a mechanical bond and USA will never migrate through the substrate’s layers.
- USA also offers a 30-40% higher yield rate per gallon than a conventional seaming solvent when applied at the recommended flow rates.
- USA is also more environmentally friendly than existing seaming solvents. The formula for USA contains 80% VOC exempt ingredients.
- Existing delivery and application methods utilized for solvent application will function flawlessly when using USA.
- Bond strength and seam clarity is equal to, and in most cases exceeds, finished shrink sleeve industry standards.