It’s the invisible part of packaging that holds everything together. Arjun Ramachandran writes on the latest in adhesives.
THE innovative world of packaging often gets excited about new shapes, labels, and materials, but amidst all the enthusiasm it is easy to forget what holds it all together.
Adhesives are quite literally the glue that holds packaging together, and play a crucial role in ensuring packaging innovations prove successful.
In turn, developments in other areas of packaging have placed greater demands on adhesives.
“We’ve seen a need for adhesives to work in a wider range of specifications,” Avery Dennison marketing manager Andrew Crawford (Australia/New Zealand) said.
“Adhesives are now expected to perform on more difficult surfaces, successfully every time, and in many cases still reduce costs.”
According to Crawford, one such difficult surface is recycled boards, which increasingly feature in the packaging produced by an environmentally conscious industry.
The influence of marketers has also changed the nature of adhesives demanded by packaging companies, says Robatech managing director Charles Graham.
“In recent times some packaging has moved from paper based products, like chip boards and eflute, towards inner packs made from plastics and other polyethylene types,” he said.
“This tends to be for higher value products like cosmetics, perfume, and jewellery, where manufacturers have spent so much money on the inner pack that they are saying: ‘Why do we need printed packaging around it? Let the bottle sell itself.’
The result is a move towards clear or plastic packaging.
“But that also means a complete change of adhesives - generally speaking, a polyurethane reactive resin is needed to seal and adhere plastic.”
Ironically, while it is preferable that adhesives are not visible to customers, their role in enhancing the visual appeal of a product is critical.
Avery Dennison’s Crawford says this is particularly true for adhesives used in labelling.
“We are trying to get end users to appreciate the value of high quality labelling in contributing to packaging that stands out on a retail shelf.”
Crawford highlights the rise in the use of pressure sensitive adhesives, which has contributed to innovative labelling solutions becoming more cost-effective.
“Marketers increasingly want a crystal-clear label - what we call the ‘no label look’,” he said.
“Five to ten years ago this was not really available due to economics, but with manufacturers swapping over to pressure sensitive adhesives, it is becoming more common.”
The “ice bucket test”, as Crawford calls it, provides a sharp example of the key role adhesives play in protecting a product’s image.
“The role of adhesives may not be obvious when first looking at a product with a white paper label, but think about a wine bottle that sits in an ice bucket at a restaurant for two hours over the course of a meal.
“Brand managers want the bottle’s label to retain its integrity for the whole meal, and always look as good as when it was bought off the shelf or first brought to them at the dinner table.
“The adhesive, and how it resists water, makes a big difference to that.”
Durability is a key feature of adhesives used in packaging today, agrees Robatech’s Graham.
“Any adhesive used for products that go into the food chain need to satisfy considerably different requirements - for example, freshness, frozen and chilled,” he said.
“The have to survive a whole range of environments - from packing sheds in places that get very hot, to a modified atmosphere situation where a product ripens slowly and reaches the consumer at peak freshness.”
Food safety also poses a challenge, says Graham, leading to many adhesive specifications highlighting compatibility with particular food regulations,
“Quite often adhesives, even if they don’t come in contact with food, are required to pass food regulations.
“For example, some potato chip bags have a rear seal that doesn’t really come in contact with potato chips, but it might be argued that there is the possibility of leaching of the adhesive, through the substrate, into the product.”
Robatech’s Charles Graham says there has been a noticeable trend towards new types of adhesives.
“We’ve seen an increase in the use of polyethylene types of adhesives over traditional Ethylene Vinyl Acetates (EVAs),” he said.
“This trend has meant that, in hot melt areas which dominate most packaging situations, there’s been a lowering of equipment maintenance as well as cleaner running environments. And, in some situations, a more effective bond.”
According to Graham, these benefits justify the greater costs of polyethylene adhesives compared with EVAs.
“The costs can be double that of EVAs, but equally can result in increased productivity and lowering of maintenance,” he said. Maintenance tasks typically focus on filters, tank cleans, application heads and nozzle blockages.
When it comes to selecting an adhesive, Graham says it is important not to fall into the trap of basing decisions on thrift.
“Many people look only at doing things cheaper,” he said.
“There’s a mentality of how close they can get to the cliff without falling off, but what they find, to their detriment, is that the cheaper option causes grief in productivity.
“They think they are saving money by opting for cheaper adhesives, but it’s important to assess total cost and waste over time, and customer satisfaction in terms of delivery and performance.
“The extra expense is usually well justified.”
Avery Dennison’s Andrew Crawford agrees, saying the greater initial materials cost of certain adhesive solutions is offset by greater flexibility.
“Pressure sensitive adhesive materials offer the flexibility to chop and change,” he said.
“It allows quick changeover on the application line, from one product to the next.
“There’s no requirement to start and stop for changeovers, or worrying about a wet glue application where there is a wait for the adhesive to warm up.”
Crawford says this flexibility is crucial, as it addresses a key trend towards smaller production runs that assist with manufacturers creating promotional runs and brand extensions.
Making shelf-ready stick
Adhesive technology has a key role to play in another major trend - shelf ready packaging.
Packaging components have changed to accommodate shelf-ready packaging, such as improvements in the quality of paper used in packaging.
Robatech’s Graham says while these changes require manufacturers to upgrade adhesives, they do already exist to suit shelf-ready packaging.
“The adhesives already exist today, but the effect to the market is an increase in cost, as it’s a better quality adhesive with higher costs associated with it.”
However, Graham says adhesives could play a greater role in the outer packaging of shelf ready products.
“Quite a lot of the outer shippers are still taped,” he said.
“Now companies are having to look at hot melt sealing because a taped box cannot be easily ripped open and presented on the shelf.
“To make it ready for shelf-ready, outer shippers will need to go through some sort of adhesive seal process.”
Not a magic potion
While adhesives are versatile, it’s still important to understand their limitations, says Avery Dennison’s Andrew Crawford.
“There’s not one adhesive that fits all applications,” he said.
“For the range of specialised applications like clear labelling, the ‘no label look’, high temperature resistance, and the ice bucket test it’s difficult to get a single adhesive that does it all.”
As customers increasingly request performance guarantees from adhesives, Robatech’s Charles Graham says greater consideration of matching adhesives to equipment is needed.
He says equipment suppliers will generally specify suitable adhesives, and acceptable viscosity ranges.
“However, while one suppliers adhesive may run on a piece of equipment and give the very best technical solution and performance, another supplier’s equivalent adhesive may offer a different level of performance.
“You just can’t pick any adhesive off the shelf, bung it in, and expect a performance guarantee.”