Adhesive Applications Flexible bonding business
While packaging may, as in the case of folding carton be viewed by some consumers as, just a box, something that holds a product in place; a box or a pouch with a printed surface where the manufacturer advertises the product, says Tom Kerchiss, chairman, RK Print Coat Instruments
M
ost consumers know that the reality in a lot more complex. Packaging must be configured appropriately, hold the product securely and
protect the contents, sometimes for long periods (such as frozen foods) until the consumer opens that pack to use the contents.
Sometimes, as with resealable, reuseable packs, protection needs to be maintained over a lengthy period. Adhesives usually coated and in small amounts are indispensible. Many of the packaging products that are available today would not be possible without modern adhesive systems. A criticism often levelled against packaging producers and brand owners is that food items are often over packed and that many of the fiddly components seem pointless and aggravating. Those of us within the industry of course know that everything is there for a reason. Many of the additional materials often considered unnecessary by consumers are there to extend the shelf life of an item, to keep cucumbers and lettuces for example, fresher for longer and reduce waste.
Pack and adhesive integrity is essential. Packaging is now regarded in many quarters as being very much at the forefront when tackling food wastage, currently estimated at around 90 million tonnes per annum in Europe. Adhesives, when poorly chosen and poorly applied ruins pack presentation. It certainly harms the brand and may even jeopardise safety. Deli- packed meats and cheeses with peel back filmic lids, which prove difficult for the consumer to open and then don’t reseal again are more than just a nuisance.
Some consumers will dispose of food and the pack if the seal refuses to reseal and when the food looks suspect. For instance, when sliced meat, or fish starts to go grey or when the filmic lid starts to cloud over and when cheese loses its moisture and begins to crumble, most consumers,
at least those who can afford too will bin it. Production machines generally lack the flexibility needed to experiment, to determine the most suitable coating applicator or other technologies for a given product run. Quality control and product development systems such as the VCM-Lab/Pilot Coater enable users to trial different materials and formulations. With a working web width of up to 300mm, the machine can print, coat and laminate on all types of flexible substrates and on a reel-to-reel basis. A wide range of selectable coating technologies and small-scale production run capability helps to enable users to realise commercial objectives and determine product or process viability.
that offers good thermal stability following curing would be necessary when laminating a retort pouch. Natural rubber lattices formulated with acrylic resins may be used for cold-seal adhesives, which are often employed in the package wrapping of heat sensitive foods such as chocolate. Adhesives have to meet many stringent requirements. Laminating adhesives for flexible packaging must for example be resistant to heat, humidity and in some instances, chemicals, which over time may affect seal integrity. Clarity and bond strength are essential. Laminating adhesives must be engineered to ensure that delamination of laminate plies does not occur. There are a variety of methods for applying a laminate adhesive including wet and dry techniques. With wet laminating the adhesive is applied to one substrate and is then co-joined with another substrate and the resulting laminate is dried. How the laminate is dried depends on the properties of the material. Exposure to heat in an oven would result in shrinkage and distortion if for example a heat sensitive polyolefin substrate were involved. With wet lamination at least one of the substrates involved must be porous, such as suitable grades of paperboard.
Ease of configurability; the acceptance of additional accessories such as corona treater; ATEX zone compliance can help organisation develop new environmentally and sustainable products; materials for a safer environment.
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 it must be remembered that film and adhesive thicknesses as well as the contents must be taken into account. For instance, there is minimal risk of absorbing migratory components with dried goods.
Many factors need to be considered when formulating or selecting an adhesive. With food packaging applications, a reactive system, one
Dry lamination differs from wet lamination in that the liquid adhesive can be applied to one substrate and then dried prior to co-joining with another material. Alternatively the adhesive can be applied as a hot melt filmic layer. In effect the adhesive becomes another layer. Bonding is obtained at high temperature and high nip pressure. The combined high heat, high nip pressure causes the adhesive to flow, which as it cools and gels results in an effective bond. Dry bond is worth considering as it can be used on a wider range of substrates including film with film and film with foil, etc. Wet and dry lamination can be undertaken on the VCML-Lab/Pilot Coater and on the K Printing Proofer and the bespoke VCM, also designed and developed by RK Print Coat Instruments.
16
July/August 2023
www.convertermag.com
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