Friendly Bonds

The growing need for safe and convenient packaging of perishable food has created a tremendous demand for flexible food packaging as a replacement for traditional rigid- and semi-rigid packaging such as steel cans and paper-based packages.

Laminate adhesives would therefore be instrumental in providing effective, better sealed packages with longer shelf life, as well as providing convenient packaging for storage and transport.


Adhesive suppliers should ensure that the composition of the laminates complies with a list of raw materials deemed as safe by the regulators. Here, an operator pours adhesives into a machine.

Sticking to safety
Advanced laminate adhesives play a foundational role in enabling lighter and more flexible packaging. They provide strong bonds with materials such as paper, plastic fi lms and aluminum foil. They ensure the efficacy of the packaging by providing airtight seams, thereby preserving the freshness, extending the shelf life, and preventing food-borne viruses in packaged food products.

In a coffee vacuum pack, aluminum foil is used as the primary barrier against moisture, oxygen and light. Mechanical strength such as tear and abrasion resistance and printability is derived from a layer of polyester film and a polyethylene film that allows bonding by hot sealing. Manufacturers would however not be able to achieve such characteristics if these materials are used alone. The layers would later be laminated with adhesives to form a new film composite material.

Polyurethane adhesives would also need to be versatile in order to store acidic food such as fruit juices and spicy sauces, as well as being resistant to heat in order to allow for sterilization of retortable pouches. And laminate adhesives have made this possible.

Safe food packaging
While flexible packaging has significantly increased the shelf life and reduced the presence of food-borne viruses in packaged foods, there are still concerns about the potential risks of polyurethane and its indirect exposure to food in the packaging process.

While polyurethane is inert and harmless to humans in its ‘cured’ state, laminates that are not cured fully contain free isocyanates (which include aliphatic and aromatic isocyanates used in formulating polyurethane laminating adhesives). They could potentially form primary aromatic amine when in contact with moisture from food, which some studies have suggested that the food might turn carcinogenic.


Smart curing adhesives do their bit for the environment due to a shorter curing process, resulting in lower energy consumption during packaging.

In 2001, a Danish business magazine reported about an independent laboratory test that was conducted to measure the levels of amines in food packaged in laminates. The results showed laminate contents of up to 100 times the official safety limits in the food. Questions were subsequently raised about the aromatic amines from polyurethane laminating adhesives that are not cured.

This led to a greater awareness and concern of the issue among companies, consumers and regulatory authorities. A number of countries responded by implementing regulations on food packaging materials, demanding that under conditions of use, no component should be transferred into the food that might endanger human health.

Adhesive suppliers should therefore ensure that the composition of the laminates complies with a list of raw materials deemed as safe by the regulators. It is also the responsibility of the converter (companies that convert materials into laminates) to provide functional barriers between adhesives and food.

The difference between the two types is that fast curing laminate adhesives provide the converter a greater flexibility and reduced cycle time for packaging food. This allows a better utilization of floor space, shorter food packaging production time, and safer packaging.

Smart adhesive laminates
Fast curing mechanisms in adhesive laminates can significantly reduce the time taken to cure the adhesives. More than 15 years ago, Henkel for example introduced solvent-based and solvent-free polyurethane adhesives with a smart curing mechanism. While typical adhesives may require up to 41 days to reach a fully ‘cured’ state deemed as safe for food packaging, smart adhesives would take a few days and are free from migratory amines.


In milk packaging for coffee and tea, aluminum foil is used as a primary barrier against moisture, oxygen and light. Mechanical strength such as tear and abrasion resistance and printability is derived from a layer of polyester film and a polyethylene film that allows bonding by hot sealing.

Responsible packaging
Smart curing adhesives do their bit for the environment due to a shorter curing process, resulting in lesser energy consumption during packaging. Using flexible packaging instead of traditional packaging materials such as steel cans, weight is also reduced, leading to greater efficiencies in transporting packaged goods.

Solvent-free adhesives on the other hand do not emit volatile organic compounds (VOCs), resulting in a safer work environment for production workers due to the lack of exposure to harmful chemicals.

Lesser energy is needed to produce the adhesives, which can deliver a 50-60% cost reduction per square meter compared to solvent-based adhesives. The substrates of such adhesives have also become thinner yet stronger. The structures have fewer layers, requiring less laminate adhesive to deliver the same packaging protection of solvent-based laminating adhesives.

Such breakthroughs are delivering significant benefits, enabling more environmentally responsible packaging and reducing costs in flexible food packaging. And while nearly half of the flexible packaging companies in Europe and the US use solvent-free adhesives, about 8% of their counterparts in Asia do. However, as more governments in Asia push for greener production, demand for solvent-free adhesives is expected to continue.

www.henkel.com