Workhorse With the Goods

Adhesives are by no means a component of packaging selected on a whim. The sticky substances are an integral element in packaging projects, and differ depending on a variety of factors that are important to the structural integrity of the packaging and, ultimately, to a consumer’s experience with a product.

Even still, adhesives aren’t exactly big headline newsmakers and they beg the question, “What’s new?” According suppliers of adhesive materials, that’s a question with good answers.

The last five years have seen innovations in the raw material components that constitute adhesives. The result of these advancements has been the development of adhesives with refined and enhanced capabilities.

Better raw materials

Aqueous, ultraviolet (UV), and electron beam (EB) are three types of adhesives and all have seen improvements due to raw material developments.

Water-based adhesives have always been the safe, non-toxic, environmentally-friendly choice. However, they have always been limited in the applications for which they were suitable. Today, new raw material alternatives have changed that.

“There has been a definite improvement in adhesives, specifically in the aqueous area,” said André DiMino, president and CEO, ADM Tronics. “This is due to a wider choice of raw material stocks over the past five years, which can now be incorporated into aqueous adhesive formulations. This has given us the ability to produce aqueous adhesives for applications which previously were only satisfied by hazardous solvent-based adhesives. Performance and application enhancements have expanded these newly available raw material choices.”

In the realm of energy-curable adhesives, UV and EB, advances have also taken place in their chemistries. In the last decade, the use of UV adhesives, inks, and coatings has become prominent. What has spurred this increased utilization is partly due to the advancements made in UV curing equipment and its growing affordability, and partly due to the improved raw material compositions of UV-cured substances.

“UV adhesives have improved dramatically in the last five years as many manufacturers of UV raw materials have developed products specifically for these applications,” said Todd Dickenscheidt, Research & Development, UVitec Printing Ink. “Also, free radical cure mechanisms are being used frequently now, where before almost all UV adhesives used cationic cure mechanisms.”

According to Dickenscheidt, this is important for two main reasons: time and application. “Cationic formulations were originally used almost exclusively because they tend to give a slower cure so that your adhesive will start very tacky and then harden after setting for a period of time. Free radical mechanisms always cure in about half a second to a given degree of tackiness. The primary advantage of free radicals is that the process has more leeway since the adhesive will stay at a certain level of tackiness after curing, allowing you to apply your label, etc., at any time,” he said. “Cationic adhesives must be applied and allowed to set at very precise dwell times. Also the cationic process is affected by humidity, so that dwell times will change as the humidity goes up or down. Cationic adhesives are still useful for applications requiring a stronger bond between substrates, however, the adhesive will dry to a very hard film instead of remaining soft like the free radical adhesives. The selection of mechanisms is based on end-product requirements, as well as ease of processing and humidity control.”

Another major contributing factor to the improvements in packaging adhesives over the past several years has come via the process by which adhesives are made, said Rick Harris, product manager, product branding business team, FLEXcon. “Adhesives go through continuous changes to meet the performance requirements of the application,” he said. “Emulsion technology has come a long way over the last 10 years to meet the market needs for performance and economics.

Despite the overall augmented capabilities of aqueous, UV, and EB adhesives, another kind of adhesive is still employed more often for the most demanding packaging jobs.

“Solvent acrylic adhesives continue to be the adhesive of choice where high performance is required and where the more difficult surface requirements and harsh environments are involved,” Harris said.

Smarter end users

Another aspect of packaging adhesives that has improved over the years is the users themselves. There seems to be a direct correlation between more knowledgeable converters and better performances in adhesives.

When it comes to choosing the most appropriate adhesive for a packaging job, users do a good job of considering all the necessary aspects in order to get the most out of the product. But there are quite a few factors that have to be looked at and, depending who is asked, the ones deemed the “most crucial” differ.

“Price and performance are major drivers in the selection of a PSA (pressure-senstive adhesive),” said Larry Slaven, vice president, general manager, 3 Sigma. “Today, end users are much better at determining the application needs. The application needs are what drive the PSA selection. For example, for outdoor high heat applications, one would choose a solvent solution acrylic, but for an indoor room temperature application, one could use a water-based emulsion acrylic or a hot melt. Not only is the adhesive the major factor in application success, but it also has a great impact on the final construction cost.”

Toal performance

All-around performance is an obvious, but important factor, according to DiMino. “An adhesive must meet the end-use application parameters for the completed structure. This includes desired adhesion level, environmental resistance properties, aesthetic effects on the final structure, and other attributes needed to assure the adhesive provides the performance required. It is interesting to note that, in most cases, the adhesive only represents a small fraction of the cost, but yet its failure can jeopardize the entire package or structure,” he said. “After performance, the next two factors would be application and cost. An adhesive must be suitable for the method of application and allow for repeatable, day-in-and-day-out production without the need for pampering or tweaking. And, of course, the cost of the adhesive must be suitable for the application.”

Harris gets more specific and names four important factors. “Printing method, dispensing method, application surface, and product life cycle requirements—all of those areas need to be reviewed,” he said. “One unknown requirement can lead to failure. The best way to approach this is to look at the entire process for each application from printing through to the end of the product life.”

Of course, cost is always a major point that has to be taken into account. This final issue of cost has become very important. In the last few years, many adhesive suppliers have had to increase the price of their products due to rising costs in raw materials and their associated chemical components, as well as the rising cost of energy, insurance, and healthcare. Those selecting and specifying these materials, now more than ever, have to compare the price of adhesives to the required performance capability in order to purchase the most cost-effective adhesive for a packaging project.

Slaven said, “Price and how it relates to performance have become issues. In the past 18 months, increased adhesive prices and supply concerns have increased the awareness of customers in determining the proper adhesive for specific applications. Price increases have been significant, demanding that customers take a more active role in comparing price and performance characteristics.”

An ‘integral’ workhorse

Adhesives are one of the workhorses of the packaging industry; they receive little attention or admiration, and yet without adhesives, packaging would literally fall apart. As packaging becomes more innovative and diverse, adhesives will only play a bigger role.

“Adhesives are one of the cornerstones of a successful application,” Harris said. “The key is to share and discuss the requirements with everyone from the adhesive supplier to the coater, to the printer, to the end user.” n