Adhesive Applications Sealing packaging securely

delamination of laminates or substrates being bonded does not occur. Delamination or tunnelling can occur when the two substrates being married together differ in extensibility and stretch or relax at different rates. Localised areas of delamination not only affect product appearance it can seriously jeopardize the food product itself. A common method of creating a


any consumers see packaging as simply a means of containing a product in a box, a carton, a flexible bag or pouch, which will be discarded when the product is used. The surface of a pack as far as most consumers are concerned is used as a vehicle for marketing purposes, which is true to some extent, but it’s more complicated than that. The pack surface or labelling aids decision-making and may contain relevant information relating (in the case of food) to ingredients, known allergies, dietary and cooking instructions, as well as use-by dates. The pack, including its component parts, should keep food items safe, secure and fresher for longer. But sometimes there is a mismatch between expectations and reality. This is when systems such as pilot coating and monitoring devices come into their own. A common criticism is that many food

products are overpacked, with fiddly components. Opening and re-sealing a so- called easy peel filmic lid can be difficult for the consumer, and this should be of concern to the brand owner and packaging technologist for several reasons. To begin with, the consumer who experiences difficulties with packaging may avoid purchasing that product or any other of the branded products in the range. But there is another important factor to consider, and that is of food wastage and packaging throwaway often contaminated with food residue. For those who can afford to do so, if there is any doubt it goes in the bin. Packaging is now regarded in many quarters as being an essential element in addressing

14 July/ August 2020

food wastage, currently estimated at around 90 million tonnes per annum in the EU. Although the relationship between shelf

life and food waste is far from straightforward knowing which product or food group spoils easiest, what brings about food loss and the perception or expectations that a consumer holds with regard to the appearance, texture and aroma and the impact on health is important for everyone in the value and supply chain. Packaging helps to preserve and protect a food item from environmental influences that may result in a deterioration in quality. Typically, the mechanisms associated with spoilage are moisture, oxygen, light and microorganisms, moulds, bacteria, etc.

MODERN ADHESIVE SYSTEMS While packaging may be viewed by some as a single entity, it is the sum of the parts, the components functioning in unison, together with of course selecting that most suitable packaging configuration for the product that determines success or failure. Adhesives, though generally coated and used in relatively small quantities are a good example. Many of the packaging products that are available today would not be possible without modern adhesive systems. Flexible packaging adhesives, the laminating adhesives for example, must provide for good clarity and bond strength. They must be resistant to heat, humidity and in some instances, chemicals that may over time affect the integrity of the seal. Adhesives must be engineered in order that

composite material that meets specific performance requirements is to laminate various polymeric materials to other films or to foils, papers, etc, with a polymeric adhesive. Waterborne polyurethane dispersions and acrylic emulsion-based laminating adhesives provide advantages over solvent borne systems and development is on-going. The monomeric portion of the polymer is recycled out prior to coating and converting. Urethanes tend to be employed in high end application critical areas, acrylics on the other hand tend to be used for applications that are not so stringent. Urethanes and acrylic waterborne can be manipulated and crosslinked increased adhesion or resistance properties. Apart from offering specific properties that enable an adhesive to perform to expectations, laminating and other adhesives associated with food, medical and custom applications must be safe to use. A greater awareness of potential

migration of components, ever changing filmic materials, both conventional and bio- based and with technology in general has meant that there is more of an emphasis on compliance and the reviewing of standards of performance. Through a balanced and objective selection, the use of monomers and the control of polymerisation, adhesives can be designed so that they are non- migratory, though there are caveats in that film and adhesive thicknesses as well as contents must be factored in. For instance, there is minimal risk of absorbing migratory components with dried goods. Fatty foods pose more of a risk so that care and attention must be exercised when selecting inks, adhesives and coatings and films. It is worth mentioning the difficulties

that polymer chemists, formulators and packaging technologists faced when developing aqueous adhesives for flexible packaging laminates. Unlike aromatic carbons, esters and other substances, which readily dissolve polymers and resins, water dissolves few of these ingredients. Furthermore, additives initially added to the dispersion or emulsion interfered with final adhesion. In time, laboratory research, shop floor trials and using pilot coating systems and other technology resulted in products that became accepted.

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