Importance of the ever-present adhesive

9 April 2018

Adhesives go largely unnoticed by consumers, but even a tiny misalignment can cause serious problems for brands. Packaging & Converting Intelligence explores the crucial role played by the sticky stuff.

Like much complex technology, packaging adhesives are superficially quite straightforward. The three main types are water-based, solvent-based and hot melt, with the use of solvents diminishing as manufacturers try to reduce volatile organic compound (VOC) emissions and improve air quality.

Water-based are the most widely used; as well as having superior air quality benefits, they are stronger, cheaper and more energy efficient, as well as being easy to use and safe for food contact. They come in natural and synthetic variants, the latter increasingly being used to label containers, make composite cans, and form and seal cartons and cases.

Use of hot melt adhesives for packaging applications continues to grow, primarily for automated carton and case sealing. This type of adhesive is totally solid; it contains no solvent or water. On the packaging line, a dispensing system applies the adhesive to a substrate such as paperboard, rigid polyethylene or film-laminated material. The adhesive dries quickly after application, forming a strong bond between the joined surfaces.

Because hot melt adhesives dry so quickly, they are most suitable for high-speed operations. This type of adhesive can also be formulated for use with a range of packaging materials, though any substrate that is sensitive to heat is a poor candidate. Processes that expose the hot melt bond to high temperatures are also not appropriate, as the heat can cause the adhesive to melt and the bond to fail.

With regard to how these three techniques fit into the current packaging landscape, Eric Post, K-FLEX global sales director, Emerald Performance Materials, says, “Many major segments, such as packaging, construction and transportation, are growing rapidly.

In response to increased demand for convenience-based goods, we have seen innovation surrounding new packaging designs for food and beverage, and other consumer items.

“Tougher structural adhesives that resist extreme environmental conditions are increasingly replacing conventional adhesives. There is also increasing global opportunity in emerging markets, such as clean energy.

“Another important consideration is the push towards waterborne adhesives and all-around lower volatility over solvent-borne adhesives, as well as the replacement of materials that could pose a threat to human health, such as phthalates, which are especially problematic in the EU, and polyfunctional aziridine cross-linkers. The Asia-Pacific region is also beginning to come more in line with North America and Europe in terms of regulation of materials.”

Eliminating solvents

Lex Reynolds, president of Reynolds Glue, agrees with Post. “There are a number of factors that can and should drive innovation over the next few years,” he says. “Eliminating the use of solvents and other suspect chemicals, such as those found in the production of polyurethanes, should be a motivating factor to those seeking alternatives.

“Products with higher heat and solvent resistance without using troublesome raw materials are of great interest. Providing alternatives to metallocene chemistry so that there are other options for compounders is important. Finally, developing cheaper raw materials will encourage innovation.”

Chris Sheeren, a partner at Huron Capital, concluded the main areas of growth would be in “regulatory changes and the end customers’ increasing demand for environmentally friendly chemicals”.

Companies must also address a shifting legal framework. “It is incredibly difficult to meet the challenge of a constantly changing regulatory landscape,” says Reynolds, “especially when a number of the forms, questionnaires and studies Reynolds has to fill out are either not directly relevant to the business or opaque to the point of needing a research PhD to be able to tackle. The company has had to take on staff whose sole role is to manage this and, if things keep going, will probably need to hire more.”

An important consideration is the push towards waterborne adhesives and all-around lower volatility over solvent-borne adhesives.

– Eric Post, Emerald Performance Materials

Sheeren agrees. “While we need to make sure that we are on top of the state-specific regulations in all of the regions in which we compete, the rules in California can be very different from those in other states,” he notes. “Trade shows and journals are a great way to keep current.”

“Over the past several years, regulatory bodies worldwide have increased their scrutiny of chemicals used in the manufacture of adhesives and sealants, with a focus on evaluating the safety and potential health effects of chemicals of concern,” says Post.

“As materials suppliers, Emerald has worked closely with customers to develop solutions that lower VOCs and eliminate materials of concern, such as phthalates and polyfunctional aziridine, a cross-linker associated with mutagenicity.”

Zero tolerance

To brand-owners, the right adhesive for their packaging is an expectation, with no tolerance for underperforming materials, particularly when it is an essentially unseen aspect of a product. Performance is only one part of it, however – environmentally responsibility is also crucial when it comes to choosing adhesives. While packaging material has been in focus for some time with regard to sustainability, brands are increasingly aware that less obvious elements are also influential.

For London-based Urban Veda, each aspect of the packaging is a marker of its brand intention. The personal-care brand manufactures all its products in the UK and favours working with suppliers across the value chain. “I had a clear vision of the final product, from the philosophy to the packaging, everything about Urban Veda reflects our holistic approach,” explains founder Sheilesh Shah. “Founded on the ancient principles of Ayurveda, all our products are naturally formulated to provide for all skin types, while factoring in the effects of environment, stress and dehydration play on our skin.”

With this philosophy underpinning the Urban Veda brand, Shah explains how every element of the product ingredients has to fit in with its values. “All the packaging is recyclable, and every bottle is made from post-consumer recycled plastic,” he says. “Recycling is like karma, what goes around comes around. Urban Veda is proud of its sourcing provenance and all of its cartons are Forest Sustainability-certified.

“It makes sense that everything used in its products is strictly controlled, so something as seemingly invisible as adhesive has its role to play in the creation of the product and brand.”

Paying close attention to details supports an overall feeling of brand identity and quality. “While Urban Veda uses block colour on its packaging, it is also fond of smaller touches and finer details,” he says.

“The company uses a range of processing while manufacturing its packaging, including matt and gloss varnishes for contrast. It also uses metallic pantones with a raised ink process to create an embossed effect.

All the packaging is recyclable, and every bottle is made from post-consumer recycled plastic. Recycling is like karma, what goes around comes around.

– Sheilesh Shah, Urban Veda

“These choices then influence the choice of adhesives; the demand for performance is as strong as the demand for responsible and sustainable packaging. A key challenge for Urban Veda is ensuring that quality and consistency across its product range when working with different suppliers.

“It is vital to always be precise and vigilant with any design briefs, and the company always performs test runs before producing large batches.”

Dr Frank Rothbarth of Covestro was keen to share a suppliers’ point of view. “Globally, solvent-free polyurethane systems are gaining importance, particularly with respect to adhesives for flexible packaging – itself a very fast-growing market,” he says.

“Water-borne polyurethane (PU) adhesives have advantages over solvent-borne systems in terms of environmental compatibility, and occupational safety and health.

“Water-borne PU dispersions can be used alone, or together with a cross-linker. They emit virtually no solvent, improving occupational safety and health.”

Creative thinking

HB Fuller, which has worked on adhesives, sealants and speciality chemical products for more than a century, is constantly on the lookout for new ways to improve technology. The company’s research and development director, Nick Lehman, says, “By bringing together adhesive specialists from different sectors to share expertise, transfer technology between markets and stimulate ideas, HB Fuller is confident it can accelerate innovation.

It provides those experts with first-class offices, laboratories, technical facilities and machinery to ensure they have the best possible environment in which to think and to create.”

By working in partnership with the downstream packaging companies in the value chain, adhesives manufacturers and suppliers can pioneer greater efficiency and sustainability.

Finding new methods to apply, dry and retain adhesives in packaging lines will help to improve the quality and production speed of consumer goods companies, while enabling any changes to form or function to be made quickly, without costly delays or disruption.

Urban Veda’s use of responsibly sourced adhesive is in line with the company’s philosophy of sustainability.
Some examples of barrier films bound with adhesives.

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